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 $57.53   10.247%   $63.4251   $63.43   $63.45   $63.40  
  Purchase #2 $84.86   9.453%   $92.8818   $92.88   $92.90   $92.90  
  Purchase #3 $200.69   6.282%   $213.2973   $213.30   $213.30   $213.30  
  Purchase #4 $216.60   12.670%   $244.0432   $244.04   $244.05   $244.00  
  Purchase #5 $127.56   12.729%   $143.7971   $143.80   $143.80   $143.80  
  Purchase #6 $36.76   12.247%   $41.262   $41.26   $41.25   $41.30  
  Purchase #7 $190.82   13.611%   $216.7925   $216.79   $216.80   $216.80  
  7 purchase totals = $914.82       $1,015.4990   $1,015.50   $1,015.55   $1,015.50