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 $43.93   5.511%   $46.351   $46.35   $46.35   $46.40  
  Purchase #2 $160.63   3.717%   $166.6006   $166.60   $166.60   $166.60  
  Purchase #3 $228.88   7.219%   $245.4028   $245.40   $245.40   $245.40  
  Purchase #4 $145.65   6.489%   $155.1012   $155.10   $155.10   $155.10  
  Purchase #5 $71.95   4.232%   $74.9949   $74.99   $75.00   $75.00  
  Purchase #6 $205.30   6.545%   $218.7369   $218.74   $218.75   $218.70  
  Purchase #7 $70.49   8.240%   $76.2984   $76.30   $76.30   $76.30  
  7 purchase totals = $926.83       $983.4858   $983.48   $983.50   $983.50