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 $203.61   9.838%   $223.6412   $223.64   $223.65   $223.60  
  Purchase #2 $165.72   8.535%   $179.8642   $179.86   $179.85   $179.90  
  Purchase #3 $9.69   13.349%   $10.9835   $10.98   $11.00   $11.00  
  Purchase #4 $218.63   10.217%   $240.9674   $240.97   $240.95   $241.00  
  Purchase #5 $48.45   5.700%   $51.2117   $51.21   $51.20   $51.20  
  Purchase #6 $218.72   13.659%   $248.595   $248.60   $248.60   $248.60  
  Purchase #7 $249.71   12.494%   $280.9088   $280.91   $280.90   $280.90  
  7 purchase totals = $1,114.53       $1,236.1718   $1,236.17   $1,236.15   $1,236.20