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 $244.27   12.605%   $275.0602   $275.06   $275.05   $275.10  
  Purchase #2 $55.67   7.808%   $60.0167   $60.02   $60.00   $60.00  
  Purchase #3 $149.60   3.122%   $154.2705   $154.27   $154.25   $154.30  
  Purchase #4 $247.79   5.542%   $261.5225   $261.52   $261.50   $261.50  
  Purchase #5 $235.99   9.788%   $259.0887   $259.09   $259.10   $259.10  
  Purchase #6 $126.53   11.178%   $140.6735   $140.67   $140.65   $140.70  
  Purchase #7 $53.79   4.625%   $56.2778   $56.28   $56.30   $56.30  
  7 purchase totals = $1,113.64       $1,206.9099   $1,206.91   $1,206.85   $1,207.00