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 $113.98   9.669%   $125.0007   $125.00   $125.00   $125.00  
  Purchase #2 $154.81   12.734%   $174.5235   $174.52   $174.50   $174.50  
  Purchase #3 $202.43   6.418%   $215.422   $215.42   $215.40   $215.40  
  Purchase #4 $57.63   8.715%   $62.6525   $62.65   $62.65   $62.70  
  Purchase #5 $167.41   10.480%   $184.9546   $184.95   $184.95   $185.00  
  Purchase #6 $85.27   13.813%   $97.0483   $97.05   $97.05   $97.00  
  Purchase #7 $134.47   11.215%   $149.5508   $149.55   $149.55   $149.60  
  7 purchase totals = $916.00       $1,009.1524   $1,009.14   $1,009.10   $1,009.20