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 $240.61   6.627%   $256.5552   $256.56   $256.55   $256.60  
  Purchase #2 $244.67   13.421%   $277.5072   $277.51   $277.50   $277.50  
  Purchase #3 $58.33   11.654%   $65.1278   $65.13   $65.15   $65.10  
  Purchase #4 $220.66   5.809%   $233.4781   $233.48   $233.50   $233.50  
  Purchase #5 $214.77   12.671%   $241.9835   $241.98   $242.00   $242.00  
  Purchase #6 $136.76   13.322%   $154.9792   $154.98   $155.00   $155.00  
  Purchase #7 $110.33   4.446%   $115.2353   $115.24   $115.25   $115.20  
  7 purchase totals = $1,226.13       $1,344.8663   $1,344.88   $1,344.95   $1,344.90