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 $223.65   13.226%   $253.2299   $253.23   $253.25   $253.20  
  Purchase #2 $127.61   10.763%   $141.3447   $141.34   $141.35   $141.30  
  Purchase #3 $147.96   10.493%   $163.4854   $163.49   $163.50   $163.50  
  Purchase #4 $14.35   12.868%   $16.1966   $16.20   $16.20   $16.20  
  Purchase #5 $188.68   10.796%   $209.0499   $209.05   $209.05   $209.00  
  Purchase #6 $204.50   9.809%   $224.5594   $224.56   $224.55   $224.60  
  Purchase #7 $20.99   6.709%   $22.3982   $22.40   $22.40   $22.40  
  7 purchase totals = $927.74       $1,030.2641   $1,030.27   $1,030.30   $1,030.20