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 $166.96   10.827%   $185.0368   $185.04   $185.05   $185.00  
  Purchase #2 $50.81   7.344%   $54.5415   $54.54   $54.55   $54.50  
  Purchase #3 $118.47   6.344%   $125.9857   $125.99   $126.00   $126.00  
  Purchase #4 $66.33   9.794%   $72.8264   $72.83   $72.85   $72.80  
  Purchase #5 $107.44   3.250%   $110.9318   $110.93   $110.95   $110.90  
  Purchase #6 $155.54   4.260%   $162.166   $162.17   $162.15   $162.20  
  Purchase #7 $240.75   3.288%   $248.6659   $248.67   $248.65   $248.70  
  7 purchase totals = $906.30       $960.1541   $960.17   $960.20   $960.10