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 $117.38   12.421%   $131.9598   $131.96   $131.95   $132.00  
  Purchase #2 $71.25   3.553%   $73.7815   $73.78   $73.80   $73.80  
  Purchase #3 $192.49   8.811%   $209.4503   $209.45   $209.45   $209.50  
  Purchase #4 $159.77   3.489%   $165.3444   $165.34   $165.35   $165.30  
  Purchase #5 $207.94   9.301%   $227.2805   $227.28   $227.30   $227.30  
  Purchase #6 $65.35   6.115%   $69.3462   $69.35   $69.35   $69.30  
  Purchase #7 $128.51   8.134%   $138.963   $138.96   $138.95   $139.00  
  7 purchase totals = $942.69       $1,016.1257   $1,016.12   $1,016.15   $1,016.20