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 $234.75   3.327%   $242.5601   $242.56   $242.55   $242.60  
  Purchase #2 $171.50   10.398%   $189.3326   $189.33   $189.35   $189.30  
  Purchase #3 $196.47   4.750%   $205.8023   $205.80   $205.80   $205.80  
  Purchase #4 $19.72   11.694%   $22.0261   $22.03   $22.05   $22.00  
  Purchase #5 $226.63   4.714%   $237.3133   $237.31   $237.30   $237.30  
  Purchase #6 $170.56   13.407%   $193.427   $193.43   $193.45   $193.40  
  Purchase #7 $162.80   13.600%   $184.9408   $184.94   $184.95   $184.90  
  7 purchase totals = $1,182.43       $1,275.4022   $1,275.40   $1,275.45   $1,275.30