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 $33.77   6.548%   $35.9813   $35.98   $36.00   $36.00  
  Purchase #2 $207.88   10.474%   $229.6534   $229.65   $229.65   $229.70  
  Purchase #3 $41.62   12.801%   $46.9478   $46.95   $46.95   $46.90  
  Purchase #4 $48.88   11.263%   $54.3854   $54.39   $54.40   $54.40  
  Purchase #5 $238.31   10.601%   $263.5732   $263.57   $263.55   $263.60  
  Purchase #6 $123.99   8.349%   $134.3419   $134.34   $134.35   $134.30  
  Purchase #7 $135.52   10.654%   $149.9583   $149.96   $149.95   $150.00  
  7 purchase totals = $829.97       $914.8413   $914.84   $914.85   $914.90