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 $87.73   7.133%   $93.9878   $93.99   $94.00   $94.00  
  Purchase #2 $211.28   9.540%   $231.4361   $231.44   $231.45   $231.40  
  Purchase #3 $139.95   6.686%   $149.3071   $149.31   $149.30   $149.30  
  Purchase #4 $141.79   3.792%   $147.1667   $147.17   $147.15   $147.20  
  Purchase #5 $133.41   7.282%   $143.1249   $143.12   $143.10   $143.10  
  Purchase #6 $175.35   5.745%   $185.4239   $185.42   $185.40   $185.40  
  Purchase #7 $61.62   7.662%   $66.3413   $66.34   $66.35   $66.30  
  7 purchase totals = $951.13       $1,016.7878   $1,016.79   $1,016.75   $1,016.70