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 $86.58   6.368%   $92.0934   $92.09   $92.10   $92.10  
  Purchase #2 $104.69   10.760%   $115.9546   $115.95   $115.95   $116.00  
  Purchase #3 $240.79   5.267%   $253.4724   $253.47   $253.45   $253.50  
  Purchase #4 $209.29   4.102%   $217.8751   $217.88   $217.90   $217.90  
  Purchase #5 $236.97   5.823%   $250.7688   $250.77   $250.75   $250.80  
  Purchase #6 $165.32   3.846%   $171.6782   $171.68   $171.70   $171.70  
  Purchase #7 $157.69   10.618%   $174.4335   $174.43   $174.45   $174.40  
  7 purchase totals = $1,201.33       $1,276.2760   $1,276.27   $1,276.30   $1,276.40