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 $47.43   13.122%   $53.6538   $53.65   $53.65   $53.70  
  Purchase #2 $194.59   6.759%   $207.7423   $207.74   $207.75   $207.70  
  Purchase #3 $179.91   3.779%   $186.7088   $186.71   $186.70   $186.70  
  Purchase #4 $32.50   10.743%   $35.9915   $35.99   $36.00   $36.00  
  Purchase #5 $203.62   13.871%   $231.8641   $231.86   $231.85   $231.90  
  Purchase #6 $244.92   9.185%   $267.4159   $267.42   $267.40   $267.40  
  Purchase #7 $51.31   6.730%   $54.7632   $54.76   $54.75   $54.80  
  7 purchase totals = $954.28       $1,038.1396   $1,038.13   $1,038.10   $1,038.20