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 $233.37   3.349%   $241.1856   $241.19   $241.20   $241.20  
  Purchase #2 $165.70   10.444%   $183.0057   $183.01   $183.00   $183.00  
  Purchase #3 $156.79   7.635%   $168.7609   $168.76   $168.75   $168.80  
  Purchase #4 $208.42   9.750%   $228.741   $228.74   $228.75   $228.70  
  Purchase #5 $209.56   3.403%   $216.6913   $216.69   $216.70   $216.70  
  Purchase #6 $224.74   11.270%   $250.0682   $250.07   $250.05   $250.10  
  Purchase #7 $209.82   8.289%   $227.212   $227.21   $227.20   $227.20  
  7 purchase totals = $1,408.40       $1,515.6647   $1,515.67   $1,515.65   $1,515.70