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 $46.46   3.556%   $48.1121   $48.11   $48.10   $48.10  
  Purchase #2 $41.95   3.122%   $43.2597   $43.26   $43.25   $43.30  
  Purchase #3 $32.36   12.292%   $36.3377   $36.34   $36.35   $36.30  
  Purchase #4 $110.29   6.726%   $117.7081   $117.71   $117.70   $117.70  
  Purchase #5 $60.48   4.297%   $63.0788   $63.08   $63.10   $63.10  
  Purchase #6 $168.48   10.280%   $185.7997   $185.80   $185.80   $185.80  
  Purchase #7 $240.34   13.434%   $272.6273   $272.63   $272.65   $272.60  
  7 purchase totals = $700.36       $766.9234   $766.93   $766.95   $766.90