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 $201.78   12.506%   $227.0146   $227.01   $227.00   $227.00  
  Purchase #2 $52.42   13.804%   $59.6561   $59.66   $59.65   $59.70  
  Purchase #3 $63.61   8.652%   $69.1135   $69.11   $69.10   $69.10  
  Purchase #4 $240.90   8.539%   $261.4705   $261.47   $261.45   $261.50  
  Purchase #5 $168.74   6.621%   $179.9123   $179.91   $179.90   $179.90  
  Purchase #6 $195.30   8.791%   $212.4688   $212.47   $212.45   $212.50  
  Purchase #7 $223.50   9.312%   $244.3123   $244.31   $244.30   $244.30  
  7 purchase totals = $1,146.25       $1,253.9481   $1,253.94   $1,253.85   $1,254.00