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 $109.54   11.844%   $122.5139   $122.51   $122.50   $122.50  
  Purchase #2 $164.86   8.233%   $178.4329   $178.43   $178.45   $178.40  
  Purchase #3 $167.34   4.109%   $174.216   $174.22   $174.20   $174.20  
  Purchase #4 $45.73   6.501%   $48.7029   $48.70   $48.70   $48.70  
  Purchase #5 $206.84   10.519%   $228.5975   $228.60   $228.60   $228.60  
  Purchase #6 $105.42   13.121%   $119.2522   $119.25   $119.25   $119.30  
  Purchase #7 $169.50   6.872%   $181.148   $181.15   $181.15   $181.10  
  7 purchase totals = $969.23       $1,052.8634   $1,052.86   $1,052.85   $1,052.80