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 $45.92   12.473%   $51.6476   $51.65   $51.65   $51.60  
  Purchase #2 $244.54   12.340%   $274.7162   $274.72   $274.70   $274.70  
  Purchase #3 $43.52   5.733%   $46.015   $46.02   $46.00   $46.00  
  Purchase #4 $233.45   3.268%   $241.0791   $241.08   $241.10   $241.10  
  Purchase #5 $153.83   10.735%   $170.3437   $170.34   $170.35   $170.30  
  Purchase #6 $11.47   10.175%   $12.6371   $12.64   $12.65   $12.60  
  Purchase #7 $186.75   12.451%   $210.0022   $210.00   $210.00   $210.00  
  7 purchase totals = $919.48       $1,006.4409   $1,006.45   $1,006.45   $1,006.30