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 $80.36   7.363%   $86.2769   $86.28   $86.30   $86.30  
  Purchase #2 $244.82   3.574%   $253.5699   $253.57   $253.55   $253.60  
  Purchase #3 $177.49   6.633%   $189.2629   $189.26   $189.25   $189.30  
  Purchase #4 $147.49   12.451%   $165.854   $165.85   $165.85   $165.90  
  Purchase #5 $197.45   3.199%   $203.7664   $203.77   $203.75   $203.80  
  Purchase #6 $242.95   9.659%   $266.4165   $266.42   $266.40   $266.40  
  Purchase #7 $55.67   10.533%   $61.5337   $61.53   $61.55   $61.50  
  7 purchase totals = $1,146.23       $1,226.6803   $1,226.68   $1,226.65   $1,226.80