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 $190.73   10.637%   $211.018   $211.02   $211.00   $211.00  
  Purchase #2 $58.70   13.239%   $66.4713   $66.47   $66.45   $66.50  
  Purchase #3 $69.40   4.839%   $72.7583   $72.76   $72.75   $72.80  
  Purchase #4 $248.68   9.499%   $272.3021   $272.30   $272.30   $272.30  
  Purchase #5 $13.31   12.511%   $14.9752   $14.98   $15.00   $15.00  
  Purchase #6 $77.27   12.212%   $86.7062   $86.71   $86.70   $86.70  
  Purchase #7 $52.85   3.338%   $54.6141   $54.61   $54.60   $54.60  
  7 purchase totals = $710.94       $778.8452   $778.85   $778.80   $778.90