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 $87.41   10.229%   $96.3512   $96.35   $96.35   $96.40  
  Purchase #2 $177.96   12.519%   $200.2388   $200.24   $200.25   $200.20  
  Purchase #3 $54.95   13.649%   $62.4501   $62.45   $62.45   $62.50  
  Purchase #4 $135.69   12.633%   $152.8317   $152.83   $152.85   $152.80  
  Purchase #5 $19.89   3.838%   $20.6534   $20.65   $20.65   $20.70  
  Purchase #6 $34.33   6.719%   $36.6366   $36.64   $36.65   $36.60  
  Purchase #7 $125.46   8.226%   $135.7803   $135.78   $135.80   $135.80  
  7 purchase totals = $635.69       $704.9421   $704.94   $705.00   $705.00