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 $227.60   11.704%   $254.2383   $254.24   $254.25   $254.20  
  Purchase #2 $221.84   12.528%   $249.6321   $249.63   $249.65   $249.60  
  Purchase #3 $52.88   11.499%   $58.9607   $58.96   $58.95   $59.00  
  Purchase #4 $97.93   9.159%   $106.8994   $106.90   $106.90   $106.90  
  Purchase #5 $33.42   13.749%   $38.0149   $38.01   $38.00   $38.00  
  Purchase #6 $122.32   6.360%   $130.0996   $130.10   $130.10   $130.10  
  Purchase #7 $154.63   6.712%   $165.0088   $165.01   $165.00   $165.00  
  7 purchase totals = $910.62       $1,002.8538   $1,002.85   $1,002.85   $1,002.80