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 $76.43   13.625%   $86.8436   $86.84   $86.85   $86.80  
  Purchase #2 $72.39   3.683%   $75.0561   $75.06   $75.05   $75.10  
  Purchase #3 $25.58   3.196%   $26.3975   $26.40   $26.40   $26.40  
  Purchase #4 $18.71   11.765%   $20.9112   $20.91   $20.90   $20.90  
  Purchase #5 $71.36   9.331%   $78.0186   $78.02   $78.00   $78.00  
  Purchase #6 $235.30   6.574%   $250.7686   $250.77   $250.75   $250.80  
  Purchase #7 $211.32   6.274%   $224.5782   $224.58   $224.60   $224.60  
  7 purchase totals = $711.09       $762.5738   $762.58   $762.55   $762.60