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 $23.42   5.144%   $24.6247   $24.62   $24.60   $24.60  
  Purchase #2 $71.83   13.692%   $81.665   $81.67   $81.65   $81.70  
  Purchase #3 $227.98   12.489%   $256.4524   $256.45   $256.45   $256.50  
  Purchase #4 $190.89   13.438%   $216.5418   $216.54   $216.55   $216.50  
  Purchase #5 $148.52   6.481%   $158.1456   $158.15   $158.15   $158.10  
  Purchase #6 $20.28   11.657%   $22.644   $22.64   $22.65   $22.60  
  Purchase #7 $177.45   13.313%   $201.0739   $201.07   $201.05   $201.10  
  7 purchase totals = $860.37       $961.1474   $961.14   $961.10   $961.10