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 $246.87   11.808%   $276.0204   $276.02   $276.00   $276.00  
  Purchase #2 $126.49   13.816%   $143.9659   $143.97   $143.95   $144.00  
  Purchase #3 $43.35   9.828%   $47.6104   $47.61   $47.60   $47.60  
  Purchase #4 $244.93   3.827%   $254.3035   $254.30   $254.30   $254.30  
  Purchase #5 $145.27   11.447%   $161.8991   $161.90   $161.90   $161.90  
  Purchase #6 $180.72   8.834%   $196.6848   $196.68   $196.70   $196.70  
  Purchase #7 $119.87   13.557%   $136.1208   $136.12   $136.10   $136.10  
  7 purchase totals = $1,107.50       $1,216.6049   $1,216.60   $1,216.55   $1,216.60