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 $68.72   12.293%   $77.1677   $77.17   $77.15   $77.20  
  Purchase #2 $237.85   3.555%   $246.3056   $246.31   $246.30   $246.30  
  Purchase #3 $118.34   5.187%   $124.4783   $124.48   $124.50   $124.50  
  Purchase #4 $50.91   11.796%   $56.9153   $56.92   $56.90   $56.90  
  Purchase #5 $93.49   6.347%   $99.4238   $99.42   $99.40   $99.40  
  Purchase #6 $226.77   11.111%   $251.9664   $251.97   $251.95   $252.00  
  Purchase #7 $11.70   5.514%   $12.3451   $12.35   $12.35   $12.30  
  7 purchase totals = $807.78       $868.6022   $868.62   $868.55   $868.60