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 $210.71   10.561%   $232.9631   $232.96   $232.95   $233.00  
  Purchase #2 $145.42   3.238%   $150.1287   $150.13   $150.15   $150.10  
  Purchase #3 $141.45   7.638%   $152.254   $152.25   $152.25   $152.30  
  Purchase #4 $243.94   7.209%   $261.5256   $261.53   $261.55   $261.50  
  Purchase #5 $227.31   11.372%   $253.1597   $253.16   $253.15   $253.20  
  Purchase #6 $7.67   4.408%   $8.0081   $8.01   $8.00   $8.00  
  Purchase #7 $207.93   13.573%   $236.1523   $236.15   $236.15   $236.20  
  7 purchase totals = $1,184.43       $1,294.1915   $1,294.19   $1,294.20   $1,294.30