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 $223.89   7.662%   $241.0445   $241.04   $241.05   $241.00  
  Purchase #2 $192.72   5.713%   $203.7301   $203.73   $203.75   $203.70  
  Purchase #3 $249.85   9.286%   $273.0511   $273.05   $273.05   $273.10  
  Purchase #4 $89.43   10.364%   $98.6985   $98.70   $98.70   $98.70  
  Purchase #5 $236.76   11.370%   $263.6796   $263.68   $263.70   $263.70  
  Purchase #6 $99.38   11.644%   $110.9518   $110.95   $110.95   $111.00  
  Purchase #7 $94.76   4.585%   $99.1047   $99.10   $99.10   $99.10  
  7 purchase totals = $1,186.79       $1,290.2603   $1,290.25   $1,290.30   $1,290.30