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 $92.75   5.202%   $97.5749   $97.57   $97.55   $97.60  
  Purchase #2 $48.34   8.711%   $52.5509   $52.55   $52.55   $52.60  
  Purchase #3 $249.25   4.820%   $261.2639   $261.26   $261.25   $261.30  
  Purchase #4 $82.27   11.408%   $91.6554   $91.66   $91.65   $91.70  
  Purchase #5 $202.27   11.493%   $225.5169   $225.52   $225.50   $225.50  
  Purchase #6 $161.69   8.104%   $174.7934   $174.79   $174.80   $174.80  
  Purchase #7 $121.54   11.292%   $135.2643   $135.26   $135.25   $135.30  
  7 purchase totals = $958.11       $1,038.6197   $1,038.61   $1,038.55   $1,038.80