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 $183.69   11.417%   $204.6619   $204.66   $204.65   $204.70  
  Purchase #2 $155.27   11.201%   $172.6618   $172.66   $172.65   $172.70  
  Purchase #3 $74.86   13.662%   $85.0874   $85.09   $85.10   $85.10  
  Purchase #4 $11.39   3.748%   $11.8169   $11.82   $11.80   $11.80  
  Purchase #5 $177.42   10.283%   $195.6641   $195.66   $195.65   $195.70  
  Purchase #6 $61.34   6.351%   $65.2357   $65.24   $65.25   $65.20  
  Purchase #7 $75.96   6.133%   $80.6186   $80.62   $80.60   $80.60  
  7 purchase totals = $739.93       $815.7464   $815.75   $815.70   $815.80