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 $86.78   11.362%   $96.6399   $96.64   $96.65   $96.60  
  Purchase #2 $240.73   11.730%   $268.9676   $268.97   $268.95   $269.00  
  Purchase #3 $110.74   12.746%   $124.8549   $124.85   $124.85   $124.90  
  Purchase #4 $150.92   10.412%   $166.6338   $166.63   $166.65   $166.60  
  Purchase #5 $247.89   12.195%   $278.1202   $278.12   $278.10   $278.10  
  Purchase #6 $67.89   5.515%   $71.6341   $71.63   $71.65   $71.60  
  Purchase #7 $41.69   11.200%   $46.3593   $46.36   $46.35   $46.40  
  7 purchase totals = $946.64       $1,053.2098   $1,053.20   $1,053.20   $1,053.20