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 $114.62   10.790%   $126.9875   $126.99   $127.00   $127.00  
  Purchase #2 $128.37   7.512%   $138.0132   $138.01   $138.00   $138.00  
  Purchase #3 $157.37   10.494%   $173.8844   $173.88   $173.90   $173.90  
  Purchase #4 $69.25   6.132%   $73.4964   $73.50   $73.50   $73.50  
  Purchase #5 $219.95   12.258%   $246.9115   $246.91   $246.90   $246.90  
  Purchase #6 $172.31   3.780%   $178.8233   $178.82   $178.80   $178.80  
  Purchase #7 $14.95   10.266%   $16.4848   $16.48   $16.50   $16.50  
  7 purchase totals = $876.82       $954.6011   $954.59   $954.60   $954.60