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 $196.93   3.746%   $204.307   $204.31   $204.30   $204.30  
  Purchase #2 $59.72   8.580%   $64.844   $64.84   $64.85   $64.80  
  Purchase #3 $246.84   13.629%   $280.4818   $280.48   $280.50   $280.50  
  Purchase #4 $126.42   5.193%   $132.985   $132.99   $133.00   $133.00  
  Purchase #5 $55.39   3.538%   $57.3497   $57.35   $57.35   $57.30  
  Purchase #6 $210.97   7.563%   $226.9257   $226.93   $226.95   $226.90  
  Purchase #7 $212.54   3.680%   $220.3615   $220.36   $220.35   $220.40  
  7 purchase totals = $1,108.81       $1,187.2547   $1,187.26   $1,187.30   $1,187.20