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 $103.74   10.308%   $114.4335   $114.43   $114.45   $114.40  
  Purchase #2 $115.32   12.568%   $129.8134   $129.81   $129.80   $129.80  
  Purchase #3 $66.25   6.838%   $70.7802   $70.78   $70.80   $70.80  
  Purchase #4 $110.79   3.281%   $114.425   $114.43   $114.45   $114.40  
  Purchase #5 $243.68   3.173%   $251.412   $251.41   $251.40   $251.40  
  Purchase #6 $101.27   13.782%   $115.227   $115.23   $115.25   $115.20  
  Purchase #7 $184.98   8.818%   $201.2915   $201.29   $201.30   $201.30  
  7 purchase totals = $926.03       $997.3826   $997.38   $997.45   $997.30