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 $57.38   7.279%   $61.5567   $61.56   $61.55   $61.60  
  Purchase #2 $245.71   11.593%   $274.1952   $274.20   $274.20   $274.20  
  Purchase #3 $175.87   5.171%   $184.9642   $184.96   $184.95   $185.00  
  Purchase #4 $131.26   8.788%   $142.7951   $142.80   $142.80   $142.80  
  Purchase #5 $66.69   5.739%   $70.5173   $70.52   $70.50   $70.50  
  Purchase #6 $110.42   7.586%   $118.7965   $118.80   $118.80   $118.80  
  Purchase #7 $221.44   12.412%   $248.9251   $248.93   $248.95   $248.90  
  7 purchase totals = $1,008.77       $1,101.7501   $1,101.77   $1,101.75   $1,101.80