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 $60.71   12.413%   $68.2459   $68.25   $68.25   $68.20  
  Purchase #2 $224.34   13.355%   $254.3006   $254.30   $254.30   $254.30  
  Purchase #3 $188.49   5.608%   $199.0605   $199.06   $199.05   $199.10  
  Purchase #4 $150.72   5.737%   $159.3668   $159.37   $159.35   $159.40  
  Purchase #5 $209.80   9.303%   $229.3177   $229.32   $229.30   $229.30  
  Purchase #6 $148.25   12.625%   $166.9666   $166.97   $166.95   $167.00  
  Purchase #7 $80.48   9.660%   $88.2544   $88.25   $88.25   $88.30  
  7 purchase totals = $1,062.79       $1,165.5125   $1,165.52   $1,165.45   $1,165.60