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 $239.49   10.655%   $265.0077   $265.01   $265.00   $265.00  
  Purchase #2 $17.47   6.373%   $18.5834   $18.58   $18.60   $18.60  
  Purchase #3 $241.82   12.547%   $272.1612   $272.16   $272.15   $272.20  
  Purchase #4 $193.59   7.364%   $207.846   $207.85   $207.85   $207.80  
  Purchase #5 $174.26   13.785%   $198.2817   $198.28   $198.30   $198.30  
  Purchase #6 $198.30   7.343%   $212.8612   $212.86   $212.85   $212.90  
  Purchase #7 $49.88   5.640%   $52.6932   $52.69   $52.70   $52.70  
  7 purchase totals = $1,114.81       $1,227.4344   $1,227.43   $1,227.45   $1,227.50