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 $98.69   12.448%   $110.9749   $110.97   $110.95   $111.00  
  Purchase #2 $113.25   7.722%   $121.9952   $122.00   $122.00   $122.00  
  Purchase #3 $210.26   6.254%   $223.4097   $223.41   $223.40   $223.40  
  Purchase #4 $71.29   8.439%   $77.3062   $77.31   $77.30   $77.30  
  Purchase #5 $11.73   5.729%   $12.402   $12.40   $12.40   $12.40  
  Purchase #6 $105.92   5.693%   $111.95   $111.95   $111.95   $112.00  
  Purchase #7 $101.73   12.369%   $114.313   $114.31   $114.30   $114.30  
  7 purchase totals = $712.87       $772.3510   $772.35   $772.30   $772.40