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 $168.65   8.145%   $182.3865   $182.39   $182.40   $182.40  
  Purchase #2 $240.59   10.863%   $266.7253   $266.73   $266.75   $266.70  
  Purchase #3 $46.35   3.631%   $48.033   $48.03   $48.05   $48.00  
  Purchase #4 $238.32   12.756%   $268.7201   $268.72   $268.70   $268.70  
  Purchase #5 $247.25   7.446%   $265.6602   $265.66   $265.65   $265.70  
  Purchase #6 $31.35   6.186%   $33.2893   $33.29   $33.30   $33.30  
  Purchase #7 $27.33   9.529%   $29.9343   $29.93   $29.95   $29.90  
  7 purchase totals = $999.84       $1,094.7487   $1,094.75   $1,094.80   $1,094.70