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 $172.63   8.312%   $186.979   $186.98   $187.00   $187.00  
  Purchase #2 $178.42   13.172%   $201.9215   $201.92   $201.90   $201.90  
  Purchase #3 $186.50   4.321%   $194.5587   $194.56   $194.55   $194.60  
  Purchase #4 $240.25   5.615%   $253.74   $253.74   $253.75   $253.70  
  Purchase #5 $230.95   11.593%   $257.724   $257.72   $257.70   $257.70  
  Purchase #6 $187.72   9.678%   $205.8875   $205.89   $205.90   $205.90  
  Purchase #7 $107.26   3.864%   $111.4045   $111.40   $111.40   $111.40  
  7 purchase totals = $1,303.73       $1,412.2152   $1,412.21   $1,412.20   $1,412.20