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   6.780%   $35.9528   $35.95   $35.95   $36.00  
  Purchase #2 $57.40   3.137%   $59.2006   $59.20   $59.20   $59.20  
  Purchase #3 $215.30   13.595%   $244.57   $244.57   $244.55   $244.60  
  Purchase #4 $118.57   7.156%   $127.0549   $127.05   $127.05   $127.10  
  Purchase #5 $207.61   6.832%   $221.7939   $221.79   $221.80   $221.80  
  Purchase #6 $245.47   10.807%   $271.9979   $272.00   $272.00   $272.00  
  Purchase #7 $16.65   12.225%   $18.6855   $18.69   $18.70   $18.70  
  7 purchase totals = $894.67       $979.2556   $979.25   $979.25   $979.40