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 $83.97   12.588%   $94.5401   $94.54   $94.55   $94.50  
  Purchase #2 $136.35   10.636%   $150.8522   $150.85   $150.85   $150.90  
  Purchase #3 $216.48   13.862%   $246.4885   $246.49   $246.50   $246.50  
  Purchase #4 $42.32   12.848%   $47.7573   $47.76   $47.75   $47.80  
  Purchase #5 $100.75   11.187%   $112.0209   $112.02   $112.00   $112.00  
  Purchase #6 $198.59   9.535%   $217.5256   $217.53   $217.55   $217.50  
  Purchase #7 $67.58   4.401%   $70.5542   $70.55   $70.55   $70.60  
  7 purchase totals = $846.04       $939.7388   $939.74   $939.75   $939.80