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 $71.92   6.119%   $76.3208   $76.32   $76.30   $76.30  
  Purchase #2 $123.98   8.254%   $134.2133   $134.21   $134.20   $134.20  
  Purchase #3 $167.28   12.662%   $188.461   $188.46   $188.45   $188.50  
  Purchase #4 $182.53   9.362%   $199.6185   $199.62   $199.60   $199.60  
  Purchase #5 $23.27   13.130%   $26.3254   $26.33   $26.35   $26.30  
  Purchase #6 $20.35   10.465%   $22.4796   $22.48   $22.50   $22.50  
  Purchase #7 $150.99   10.704%   $167.152   $167.15   $167.15   $167.20  
  7 purchase totals = $740.32       $814.5706   $814.57   $814.55   $814.60