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 $55.32   7.673%   $59.5647   $59.56   $59.55   $59.60  
  Purchase #2 $117.53   13.215%   $133.0616   $133.06   $133.05   $133.10  
  Purchase #3 $178.64   8.798%   $194.3567   $194.36   $194.35   $194.40  
  Purchase #4 $32.25   10.546%   $35.6511   $35.65   $35.65   $35.70  
  Purchase #5 $153.98   12.254%   $172.8487   $172.85   $172.85   $172.80  
  Purchase #6 $192.86   4.631%   $201.7913   $201.79   $201.80   $201.80  
  Purchase #7 $13.29   12.574%   $14.9611   $14.96   $14.95   $15.00  
  7 purchase totals = $743.87       $812.2352   $812.23   $812.20   $812.40