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 $217.81   8.349%   $235.995   $236.00   $236.00   $236.00  
  Purchase #2 $224.30   13.502%   $254.585   $254.59   $254.60   $254.60  
  Purchase #3 $207.94   6.153%   $220.7345   $220.73   $220.75   $220.70  
  Purchase #4 $165.42   12.706%   $186.4383   $186.44   $186.45   $186.40  
  Purchase #5 $177.79   12.463%   $199.948   $199.95   $199.95   $199.90  
  Purchase #6 $66.43   5.745%   $70.2464   $70.25   $70.25   $70.20  
  Purchase #7 $19.90   9.706%   $21.8315   $21.83   $21.85   $21.80  
  7 purchase totals = $1,079.59       $1,189.7787   $1,189.79   $1,189.85   $1,189.60