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 $62.34   5.820%   $65.9682   $65.97   $65.95   $66.00  
  Purchase #2 $53.63   7.851%   $57.8405   $57.84   $57.85   $57.80  
  Purchase #3 $35.59   6.132%   $37.7724   $37.77   $37.75   $37.80  
  Purchase #4 $95.32   7.770%   $102.7264   $102.73   $102.75   $102.70  
  Purchase #5 $150.46   6.651%   $160.4671   $160.47   $160.45   $160.50  
  Purchase #6 $44.49   10.846%   $49.3154   $49.32   $49.30   $49.30  
  Purchase #7 $143.28   13.317%   $162.3606   $162.36   $162.35   $162.40  
  7 purchase totals = $585.11       $636.4506   $636.46   $636.40   $636.50