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 $79.53   7.118%   $85.1909   $85.19   $85.20   $85.20  
  Purchase #2 $159.84   12.148%   $179.2574   $179.26   $179.25   $179.30  
  Purchase #3 $145.77   5.667%   $154.0308   $154.03   $154.05   $154.00  
  Purchase #4 $124.37   13.598%   $141.2818   $141.28   $141.30   $141.30  
  Purchase #5 $62.44   12.784%   $70.4223   $70.42   $70.40   $70.40  
  Purchase #6 $118.76   9.710%   $130.2916   $130.29   $130.30   $130.30  
  Purchase #7 $241.29   5.223%   $253.8926   $253.89   $253.90   $253.90  
  7 purchase totals = $932.00       $1,014.3674   $1,014.36   $1,014.40   $1,014.40