Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $166.78   11.197%   $185.4544   $185.45   $185.45   $185.50  
  Purchase #2 $222.85   4.396%   $232.6465   $232.65   $232.65   $232.60  
  Purchase #3 $157.40   4.618%   $164.6687   $164.67   $164.65   $164.70  
  Purchase #4 $115.37   8.206%   $124.8373   $124.84   $124.85   $124.80  
  Purchase #5 $157.78   11.263%   $175.5508   $175.55   $175.55   $175.60  
  Purchase #6 $116.35   5.240%   $122.4467   $122.45   $122.45   $122.40  
  Purchase #7 $240.27   9.145%   $262.2427   $262.24   $262.25   $262.20  
  7 purchase totals = $1,176.80       $1,267.8471   $1,267.85   $1,267.85   $1,267.80