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 $86.29   10.697%   $95.5204   $95.52   $95.50   $95.50  
  Purchase #2 $64.97   8.116%   $70.243   $70.24   $70.25   $70.20  
  Purchase #3 $66.53   12.187%   $74.638   $74.64   $74.65   $74.60  
  Purchase #4 $231.49   8.733%   $251.706   $251.71   $251.70   $251.70  
  Purchase #5 $218.89   6.140%   $232.3298   $232.33   $232.35   $232.30  
  Purchase #6 $209.81   8.230%   $227.0774   $227.08   $227.10   $227.10  
  Purchase #7 $36.48   7.147%   $39.0872   $39.09   $39.10   $39.10  
  7 purchase totals = $914.46       $990.6018   $990.61   $990.65   $990.50