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 $49.57   9.310%   $54.185   $54.19   $54.20   $54.20  
  Purchase #2 $94.33   12.193%   $105.8317   $105.83   $105.85   $105.80  
  Purchase #3 $97.34   5.612%   $102.8027   $102.80   $102.80   $102.80  
  Purchase #4 $229.53   7.390%   $246.4923   $246.49   $246.50   $246.50  
  Purchase #5 $94.84   6.472%   $100.978   $100.98   $101.00   $101.00  
  Purchase #6 $57.81   12.389%   $64.9721   $64.97   $64.95   $65.00  
  Purchase #7 $20.45   12.407%   $22.9872   $22.99   $23.00   $23.00  
  7 purchase totals = $643.87       $698.2490   $698.25   $698.30   $698.30