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 $216.96   11.360%   $241.6067   $241.61   $241.60   $241.60  
  Purchase #2 $193.74   7.551%   $208.3693   $208.37   $208.35   $208.40  
  Purchase #3 $225.78   12.410%   $253.7993   $253.80   $253.80   $253.80  
  Purchase #4 $151.27   10.496%   $167.1473   $167.15   $167.15   $167.10  
  Purchase #5 $71.53   9.302%   $78.1837   $78.18   $78.20   $78.20  
  Purchase #6 $244.67   3.588%   $253.4488   $253.45   $253.45   $253.40  
  Purchase #7 $179.62   8.544%   $194.9667   $194.97   $194.95   $195.00  
  7 purchase totals = $1,283.57       $1,397.5218   $1,397.53   $1,397.50   $1,397.50