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 $56.41   11.589%   $62.9474   $62.95   $62.95   $62.90  
  Purchase #2 $131.53   7.156%   $140.9423   $140.94   $140.95   $140.90  
  Purchase #3 $129.47   12.554%   $145.7237   $145.72   $145.70   $145.70  
  Purchase #4 $11.34   4.568%   $11.858   $11.86   $11.85   $11.90  
  Purchase #5 $160.26   6.204%   $170.2025   $170.20   $170.20   $170.20  
  Purchase #6 $214.80   6.549%   $228.8673   $228.87   $228.85   $228.90  
  Purchase #7 $160.74   9.171%   $175.4815   $175.48   $175.50   $175.50  
  7 purchase totals = $864.55       $936.0227   $936.02   $936.00   $936.00