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 $86.42   11.516%   $96.3721   $96.37   $96.35   $96.40  
  Purchase #2 $118.83   10.558%   $131.3761   $131.38   $131.40   $131.40  
  Purchase #3 $250.61   4.627%   $262.2057   $262.21   $262.20   $262.20  
  Purchase #4 $9.65   5.640%   $10.1943   $10.19   $10.20   $10.20  
  Purchase #5 $94.83   8.268%   $102.6705   $102.67   $102.65   $102.70  
  Purchase #6 $245.34   10.265%   $270.5242   $270.52   $270.50   $270.50  
  Purchase #7 $108.64   8.679%   $118.0689   $118.07   $118.05   $118.10  
  7 purchase totals = $914.32       $991.4118   $991.41   $991.35   $991.50