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 $239.70   9.488%   $262.4427   $262.44   $262.45   $262.40  
  Purchase #2 $132.67   9.560%   $145.3533   $145.35   $145.35   $145.40  
  Purchase #3 $70.95   6.832%   $75.7973   $75.80   $75.80   $75.80  
  Purchase #4 $170.85   13.362%   $193.679   $193.68   $193.70   $193.70  
  Purchase #5 $44.32   9.524%   $48.541   $48.54   $48.55   $48.50  
  Purchase #6 $66.93   12.753%   $75.4656   $75.47   $75.45   $75.50  
  Purchase #7 $72.38   4.822%   $75.8702   $75.87   $75.85   $75.90  
  7 purchase totals = $797.80       $877.1491   $877.15   $877.15   $877.20