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 $55.72   10.734%   $61.701   $61.70   $61.70   $61.70  
  Purchase #2 $203.35   11.461%   $226.6559   $226.66   $226.65   $226.70  
  Purchase #3 $7.66   4.858%   $8.0321   $8.03   $8.05   $8.00  
  Purchase #4 $70.87   7.728%   $76.3468   $76.35   $76.35   $76.30  
  Purchase #5 $143.39   9.563%   $157.1024   $157.10   $157.10   $157.10  
  Purchase #6 $232.73   9.412%   $254.6345   $254.63   $254.65   $254.60  
  Purchase #7 $167.58   7.529%   $180.1971   $180.20   $180.20   $180.20  
  7 purchase totals = $881.30       $964.6698   $964.67   $964.70   $964.60