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 $241.97   8.605%   $262.7915   $262.79   $262.80   $262.80  
  Purchase #2 $153.76   7.533%   $165.3427   $165.34   $165.35   $165.30  
  Purchase #3 $239.72   10.249%   $264.2889   $264.29   $264.30   $264.30  
  Purchase #4 $73.92   9.414%   $80.8788   $80.88   $80.90   $80.90  
  Purchase #5 $208.34   9.389%   $227.901   $227.90   $227.90   $227.90  
  Purchase #6 $234.32   12.131%   $262.7454   $262.75   $262.75   $262.70  
  Purchase #7 $230.35   5.228%   $242.3927   $242.39   $242.40   $242.40  
  7 purchase totals = $1,382.38       $1,506.3410   $1,506.34   $1,506.40   $1,506.30