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 $206.60   11.175%   $229.6876   $229.69   $229.70   $229.70  
  Purchase #2 $143.47   5.279%   $151.0438   $151.04   $151.05   $151.00  
  Purchase #3 $228.26   5.853%   $241.6201   $241.62   $241.60   $241.60  
  Purchase #4 $94.50   5.529%   $99.7249   $99.72   $99.70   $99.70  
  Purchase #5 $86.35   8.857%   $93.998   $94.00   $94.00   $94.00  
  Purchase #6 $7.26   10.813%   $8.045   $8.05   $8.05   $8.00  
  Purchase #7 $126.40   4.170%   $131.6709   $131.67   $131.65   $131.70  
  7 purchase totals = $892.84       $955.7903   $955.79   $955.75   $955.70