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 $234.86   5.260%   $247.2136   $247.21   $247.20   $247.20  
  Purchase #2 $6.68   8.691%   $7.2606   $7.26   $7.25   $7.30  
  Purchase #3 $159.41   8.801%   $173.4397   $173.44   $173.45   $173.40  
  Purchase #4 $101.55   9.443%   $111.1394   $111.14   $111.15   $111.10  
  Purchase #5 $173.52   13.444%   $196.848   $196.85   $196.85   $196.80  
  Purchase #6 $122.78   10.133%   $135.2213   $135.22   $135.20   $135.20  
  Purchase #7 $182.86   6.257%   $194.3016   $194.30   $194.30   $194.30  
  7 purchase totals = $981.66       $1,065.4242   $1,065.42   $1,065.40   $1,065.30