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 $103.32   10.686%   $114.3608   $114.36   $114.35   $114.40  
  Purchase #2 $48.45   13.227%   $54.8585   $54.86   $54.85   $54.90  
  Purchase #3 $232.32   4.491%   $242.7535   $242.75   $242.75   $242.80  
  Purchase #4 $165.54   6.776%   $176.757   $176.76   $176.75   $176.80  
  Purchase #5 $101.75   8.227%   $110.121   $110.12   $110.10   $110.10  
  Purchase #6 $172.64   9.843%   $189.633   $189.63   $189.65   $189.60  
  Purchase #7 $119.83   12.861%   $135.2413   $135.24   $135.25   $135.20  
  7 purchase totals = $943.85       $1,023.7251   $1,023.72   $1,023.70   $1,023.80