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 $222.32   13.364%   $252.0308   $252.03   $252.05   $252.00  
  Purchase #2 $95.43   9.240%   $104.2477   $104.25   $104.25   $104.20  
  Purchase #3 $91.80   10.762%   $101.6795   $101.68   $101.70   $101.70  
  Purchase #4 $233.27   11.455%   $259.9911   $259.99   $260.00   $260.00  
  Purchase #5 $217.39   7.270%   $233.1943   $233.19   $233.20   $233.20  
  Purchase #6 $118.94   9.134%   $129.804   $129.80   $129.80   $129.80  
  Purchase #7 $154.45   3.792%   $160.3067   $160.31   $160.30   $160.30  
  7 purchase totals = $1,133.60       $1,241.2541   $1,241.25   $1,241.30   $1,241.20