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 $62.41   6.472%   $66.4492   $66.45   $66.45   $66.40  
  Purchase #2 $167.32   12.366%   $188.0108   $188.01   $188.00   $188.00  
  Purchase #3 $223.42   10.266%   $246.3563   $246.36   $246.35   $246.40  
  Purchase #4 $152.28   12.187%   $170.8384   $170.84   $170.85   $170.80  
  Purchase #5 $87.57   5.838%   $92.6823   $92.68   $92.70   $92.70  
  Purchase #6 $12.29   4.597%   $12.855   $12.86   $12.85   $12.90  
  Purchase #7 $20.98   10.363%   $23.1542   $23.15   $23.15   $23.20  
  7 purchase totals = $726.27       $800.3462   $800.35   $800.35   $800.40