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 $248.35   9.503%   $271.9507   $271.95   $271.95   $272.00  
  Purchase #2 $115.98   8.282%   $125.5855   $125.59   $125.60   $125.60  
  Purchase #3 $146.57   13.211%   $165.9334   $165.93   $165.95   $165.90  
  Purchase #4 $168.48   5.774%   $178.208   $178.21   $178.20   $178.20  
  Purchase #5 $75.48   13.581%   $85.7309   $85.73   $85.75   $85.70  
  Purchase #6 $141.89   7.274%   $152.2111   $152.21   $152.20   $152.20  
  Purchase #7 $205.82   12.832%   $232.2308   $232.23   $232.25   $232.20  
  7 purchase totals = $1,102.57       $1,211.8504   $1,211.85   $1,211.90   $1,211.80