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 $235.36   13.461%   $267.0418   $267.04   $267.05   $267.00  
  Purchase #2 $228.44   10.240%   $251.8323   $251.83   $251.85   $251.80  
  Purchase #3 $48.53   13.617%   $55.1383   $55.14   $55.15   $55.10  
  Purchase #4 $138.79   9.145%   $151.4823   $151.48   $151.50   $151.50  
  Purchase #5 $29.39   4.448%   $30.6973   $30.70   $30.70   $30.70  
  Purchase #6 $236.70   11.349%   $263.5631   $263.56   $263.55   $263.60  
  Purchase #7 $237.94   5.750%   $251.6216   $251.62   $251.60   $251.60  
  7 purchase totals = $1,155.15       $1,271.3767   $1,271.37   $1,271.40   $1,271.30