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 $33.67   3.683%   $34.9101   $34.91   $34.90   $34.90  
  Purchase #2 $178.77   11.740%   $199.7576   $199.76   $199.75   $199.80  
  Purchase #3 $200.66   13.664%   $228.0782   $228.08   $228.10   $228.10  
  Purchase #4 $245.78   9.638%   $269.4683   $269.47   $269.45   $269.50  
  Purchase #5 $111.58   4.165%   $116.2273   $116.23   $116.25   $116.20  
  Purchase #6 $142.51   5.221%   $149.9504   $149.95   $149.95   $150.00  
  Purchase #7 $180.38   9.286%   $197.1301   $197.13   $197.15   $197.10  
  7 purchase totals = $1,093.35       $1,195.5220   $1,195.53   $1,195.55   $1,195.60