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 $190.57   9.783%   $209.2135   $209.21   $209.20   $209.20  
  Purchase #2 $86.85   6.365%   $92.378   $92.38   $92.40   $92.40  
  Purchase #3 $48.65   6.334%   $51.7315   $51.73   $51.75   $51.70  
  Purchase #4 $225.96   6.772%   $241.262   $241.26   $241.25   $241.30  
  Purchase #5 $233.72   11.341%   $260.2262   $260.23   $260.25   $260.20  
  Purchase #6 $176.30   4.856%   $184.8611   $184.86   $184.85   $184.90  
  Purchase #7 $143.31   5.369%   $151.0043   $151.00   $151.00   $151.00  
  7 purchase totals = $1,105.36       $1,190.6766   $1,190.67   $1,190.70   $1,190.70