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 $226.49   8.623%   $246.0202   $246.02   $246.00   $246.00  
  Purchase #2 $100.34   10.175%   $110.5496   $110.55   $110.55   $110.50  
  Purchase #3 $121.39   13.832%   $138.1807   $138.18   $138.20   $138.20  
  Purchase #4 $80.37   5.569%   $84.8458   $84.85   $84.85   $84.80  
  Purchase #5 $148.62   5.196%   $156.3423   $156.34   $156.35   $156.30  
  Purchase #6 $197.75   9.751%   $217.0326   $217.03   $217.05   $217.00  
  Purchase #7 $48.69   3.464%   $50.3766   $50.38   $50.40   $50.40  
  7 purchase totals = $923.65       $1,003.3478   $1,003.35   $1,003.40   $1,003.20