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 $160.81   11.201%   $178.8223   $178.82   $178.80   $178.80  
  Purchase #2 $215.38   13.411%   $244.2646   $244.26   $244.25   $244.30  
  Purchase #3 $118.64   4.845%   $124.3881   $124.39   $124.40   $124.40  
  Purchase #4 $145.86   12.264%   $163.7483   $163.75   $163.75   $163.70  
  Purchase #5 $191.58   13.300%   $217.0601   $217.06   $217.05   $217.10  
  Purchase #6 $79.41   11.687%   $88.6906   $88.69   $88.70   $88.70  
  Purchase #7 $43.40   11.240%   $48.2782   $48.28   $48.30   $48.30  
  7 purchase totals = $955.08       $1,065.2522   $1,065.25   $1,065.25   $1,065.30