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 $227.34   10.619%   $251.4812   $251.48   $251.50   $251.50  
  Purchase #2 $221.52   6.514%   $235.9498   $235.95   $235.95   $235.90  
  Purchase #3 $72.66   6.549%   $77.4185   $77.42   $77.40   $77.40  
  Purchase #4 $174.92   5.680%   $184.8555   $184.86   $184.85   $184.90  
  Purchase #5 $53.81   12.687%   $60.6369   $60.64   $60.65   $60.60  
  Purchase #6 $197.85   7.104%   $211.9053   $211.91   $211.90   $211.90  
  Purchase #7 $176.56   6.377%   $187.8192   $187.82   $187.80   $187.80  
  7 purchase totals = $1,124.66       $1,210.0664   $1,210.08   $1,210.05   $1,210.00