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 $24.69   11.740%   $27.5886   $27.59   $27.60   $27.60  
  Purchase #2 $101.49   5.428%   $106.9989   $107.00   $107.00   $107.00  
  Purchase #3 $79.36   12.633%   $89.3855   $89.39   $89.40   $89.40  
  Purchase #4 $249.85   7.782%   $269.2933   $269.29   $269.30   $269.30  
  Purchase #5 $162.49   10.734%   $179.9317   $179.93   $179.95   $179.90  
  Purchase #6 $60.45   9.386%   $66.1238   $66.12   $66.10   $66.10  
  Purchase #7 $84.61   9.422%   $92.582   $92.58   $92.60   $92.60  
  7 purchase totals = $762.94       $831.9038   $831.90   $831.95   $831.90