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 $234.76   13.858%   $267.293   $267.29   $267.30   $267.30  
  Purchase #2 $159.76   13.624%   $181.5257   $181.53   $181.55   $181.50  
  Purchase #3 $23.66   7.222%   $25.3687   $25.37   $25.35   $25.40  
  Purchase #4 $14.93   5.593%   $15.765   $15.77   $15.75   $15.80  
  Purchase #5 $122.30   13.803%   $139.1811   $139.18   $139.20   $139.20  
  Purchase #6 $197.69   7.132%   $211.7893   $211.79   $211.80   $211.80  
  Purchase #7 $85.59   5.206%   $90.0458   $90.05   $90.05   $90.00  
  7 purchase totals = $838.69       $930.9686   $930.98   $931.00   $931.00