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 $202.65   6.197%   $215.2082   $215.21   $215.20   $215.20  
  Purchase #2 $183.61   13.616%   $208.6103   $208.61   $208.60   $208.60  
  Purchase #3 $101.75   9.165%   $111.0754   $111.08   $111.10   $111.10  
  Purchase #4 $244.51   6.247%   $259.7845   $259.78   $259.80   $259.80  
  Purchase #5 $137.53   10.807%   $152.3929   $152.39   $152.40   $152.40  
  Purchase #6 $238.57   5.848%   $252.5216   $252.52   $252.50   $252.50  
  Purchase #7 $182.59   6.258%   $194.0165   $194.02   $194.00   $194.00  
  7 purchase totals = $1,291.21       $1,393.6094   $1,393.61   $1,393.60   $1,393.60