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 $195.32   8.831%   $212.5687   $212.57   $212.55   $212.60  
  Purchase #2 $45.31   7.810%   $48.8487   $48.85   $48.85   $48.80  
  Purchase #3 $211.94   4.246%   $220.939   $220.94   $220.95   $220.90  
  Purchase #4 $217.34   11.776%   $242.934   $242.93   $242.95   $242.90  
  Purchase #5 $63.63   8.869%   $69.2733   $69.27   $69.25   $69.30  
  Purchase #6 $173.25   7.811%   $186.7826   $186.78   $186.80   $186.80  
  Purchase #7 $16.45   13.722%   $18.7073   $18.71   $18.70   $18.70  
  7 purchase totals = $923.24       $1,000.0536   $1,000.05   $1,000.05   $1,000.00