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 $154.56   13.414%   $175.2927   $175.29   $175.30   $175.30  
  Purchase #2 $43.93   12.214%   $49.2956   $49.30   $49.30   $49.30  
  Purchase #3 $97.30   13.538%   $110.4725   $110.47   $110.45   $110.50  
  Purchase #4 $134.28   10.503%   $148.3834   $148.38   $148.40   $148.40  
  Purchase #5 $65.94   12.803%   $74.3823   $74.38   $74.40   $74.40  
  Purchase #6 $215.77   9.847%   $237.0169   $237.02   $237.00   $237.00  
  Purchase #7 $233.25   5.495%   $246.0671   $246.07   $246.05   $246.10  
  7 purchase totals = $945.03       $1,040.9105   $1,040.91   $1,040.90   $1,041.00