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 $119.29   11.518%   $133.0298   $133.03   $133.05   $133.00  
  Purchase #2 $172.59   9.344%   $188.7168   $188.72   $188.70   $188.70  
  Purchase #3 $186.97   7.484%   $200.9628   $200.96   $200.95   $201.00  
  Purchase #4 $203.27   9.717%   $223.0217   $223.02   $223.00   $223.00  
  Purchase #5 $247.49   7.483%   $266.0097   $266.01   $266.00   $266.00  
  Purchase #6 $52.55   5.457%   $55.4177   $55.42   $55.40   $55.40  
  Purchase #7 $195.38   9.652%   $214.2381   $214.24   $214.25   $214.20  
  7 purchase totals = $1,177.54       $1,281.3966   $1,281.40   $1,281.35   $1,281.30