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 $244.27   10.217%   $269.2271   $269.23   $269.25   $269.20  
  Purchase #2 $214.82   5.716%   $227.0991   $227.10   $227.10   $227.10  
  Purchase #3 $88.58   8.407%   $96.0269   $96.03   $96.05   $96.00  
  Purchase #4 $45.46   9.294%   $49.6851   $49.69   $49.70   $49.70  
  Purchase #5 $18.33   8.835%   $19.9495   $19.95   $19.95   $19.90  
  Purchase #6 $126.96   5.746%   $134.2551   $134.26   $134.25   $134.30  
  Purchase #7 $74.43   8.757%   $80.9478   $80.95   $80.95   $80.90  
  7 purchase totals = $812.85       $877.1906   $877.21   $877.25   $877.10