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 $87.65   7.842%   $94.5235   $94.52   $94.50   $94.50  
  Purchase #2 $74.94   9.797%   $82.2819   $82.28   $82.30   $82.30  
  Purchase #3 $45.50   6.365%   $48.3961   $48.40   $48.40   $48.40  
  Purchase #4 $234.65   3.800%   $243.5667   $243.57   $243.55   $243.60  
  Purchase #5 $171.27   7.714%   $184.4818   $184.48   $184.50   $184.50  
  Purchase #6 $46.37   6.659%   $49.4578   $49.46   $49.45   $49.50  
  Purchase #7 $153.88   12.835%   $173.6305   $173.63   $173.65   $173.60  
  7 purchase totals = $814.26       $876.3383   $876.34   $876.35   $876.40