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 $201.66   7.198%   $216.1755   $216.18   $216.20   $216.20  
  Purchase #2 $108.75   6.679%   $116.0134   $116.01   $116.00   $116.00  
  Purchase #3 $202.63   10.166%   $223.2294   $223.23   $223.25   $223.20  
  Purchase #4 $156.35   10.591%   $172.909   $172.91   $172.90   $172.90  
  Purchase #5 $242.60   4.155%   $252.68   $252.68   $252.70   $252.70  
  Purchase #6 $140.80   3.366%   $145.5393   $145.54   $145.55   $145.50  
  Purchase #7 $141.41   6.301%   $150.3202   $150.32   $150.30   $150.30  
  7 purchase totals = $1,194.20       $1,276.8668   $1,276.87   $1,276.90   $1,276.80