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 $65.97   8.454%   $71.5471   $71.55   $71.55   $71.50  
  Purchase #2 $201.51   8.424%   $218.4852   $218.49   $218.50   $218.50  
  Purchase #3 $82.93   5.519%   $87.5069   $87.51   $87.50   $87.50  
  Purchase #4 $127.65   10.674%   $141.2754   $141.28   $141.30   $141.30  
  Purchase #5 $118.38   5.216%   $124.5547   $124.55   $124.55   $124.60  
  Purchase #6 $108.48   11.644%   $121.1114   $121.11   $121.10   $121.10  
  Purchase #7 $233.47   11.464%   $260.235   $260.24   $260.25   $260.20  
  7 purchase totals = $938.39       $1,024.7157   $1,024.73   $1,024.75   $1,024.70