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 $102.37   11.306%   $113.944   $113.94   $113.95   $113.90  
  Purchase #2 $184.82   9.796%   $202.925   $202.93   $202.95   $202.90  
  Purchase #3 $13.38   10.501%   $14.785   $14.79   $14.80   $14.80  
  Purchase #4 $146.50   11.603%   $163.4984   $163.50   $163.50   $163.50  
  Purchase #5 $85.34   13.553%   $96.9061   $96.91   $96.90   $96.90  
  Purchase #6 $89.77   13.836%   $102.1906   $102.19   $102.20   $102.20  
  Purchase #7 $219.83   11.156%   $244.3542   $244.35   $244.35   $244.40  
  7 purchase totals = $842.01       $938.6033   $938.61   $938.65   $938.60