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 $50.94   13.282%   $57.7059   $57.71   $57.70   $57.70  
  Purchase #2 $242.68   9.582%   $265.9336   $265.93   $265.95   $265.90  
  Purchase #3 $73.56   3.759%   $76.3251   $76.33   $76.35   $76.30  
  Purchase #4 $168.45   6.322%   $179.0994   $179.10   $179.10   $179.10  
  Purchase #5 $86.78   11.791%   $97.0122   $97.01   $97.00   $97.00  
  Purchase #6 $217.42   3.324%   $224.647   $224.65   $224.65   $224.60  
  Purchase #7 $131.74   7.419%   $141.5138   $141.51   $141.50   $141.50  
  7 purchase totals = $971.57       $1,042.2370   $1,042.24   $1,042.25   $1,042.10