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 $216.81   9.661%   $237.756   $237.76   $237.75   $237.80  
  Purchase #2 $53.46   6.190%   $56.7692   $56.77   $56.75   $56.80  
  Purchase #3 $40.26   11.206%   $44.7715   $44.77   $44.75   $44.80  
  Purchase #4 $197.84   4.382%   $206.5093   $206.51   $206.50   $206.50  
  Purchase #5 $7.91   3.142%   $8.1585   $8.16   $8.15   $8.20  
  Purchase #6 $237.52   10.426%   $262.2838   $262.28   $262.30   $262.30  
  Purchase #7 $100.86   13.507%   $114.4832   $114.48   $114.50   $114.50  
  7 purchase totals = $854.66       $930.7315   $930.73   $930.70   $930.90