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 $115.64   10.277%   $127.5243   $127.52   $127.50   $127.50  
  Purchase #2 $174.54   10.701%   $193.2175   $193.22   $193.20   $193.20  
  Purchase #3 $234.37   4.222%   $244.2651   $244.27   $244.25   $244.30  
  Purchase #4 $249.42   9.343%   $272.7233   $272.72   $272.70   $272.70  
  Purchase #5 $79.68   9.335%   $87.1181   $87.12   $87.10   $87.10  
  Purchase #6 $247.63   11.587%   $276.3229   $276.32   $276.30   $276.30  
  Purchase #7 $175.42   4.267%   $182.9052   $182.91   $182.90   $182.90  
  7 purchase totals = $1,276.70       $1,384.0764   $1,384.08   $1,383.95   $1,384.00