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 $58.49   6.749%   $62.4375   $62.44   $62.45   $62.40  
  Purchase #2 $5.50   11.336%   $6.1235   $6.12   $6.10   $6.10  
  Purchase #3 $96.64   12.465%   $108.6862   $108.69   $108.70   $108.70  
  Purchase #4 $159.81   7.482%   $171.767   $171.77   $171.75   $171.80  
  Purchase #5 $247.95   9.268%   $270.93   $270.93   $270.95   $270.90  
  Purchase #6 $40.84   12.340%   $45.8797   $45.88   $45.90   $45.90  
  Purchase #7 $177.95   10.812%   $197.19   $197.19   $197.20   $197.20  
  7 purchase totals = $787.18       $863.0139   $863.02   $863.05   $863.00