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 $190.39   11.656%   $212.5819   $212.58   $212.60   $212.60  
  Purchase #2 $152.38   6.215%   $161.8504   $161.85   $161.85   $161.90  
  Purchase #3 $102.32   11.435%   $114.0203   $114.02   $114.00   $114.00  
  Purchase #4 $203.96   6.515%   $217.248   $217.25   $217.25   $217.20  
  Purchase #5 $6.48   5.181%   $6.8157   $6.82   $6.80   $6.80  
  Purchase #6 $177.73   5.443%   $187.4038   $187.40   $187.40   $187.40  
  Purchase #7 $123.91   9.770%   $136.016   $136.02   $136.00   $136.00  
  7 purchase totals = $957.17       $1,035.9361   $1,035.94   $1,035.90   $1,035.90