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 $116.42   8.716%   $126.5672   $126.57   $126.55   $126.60  
  Purchase #2 $246.44   7.852%   $265.7905   $265.79   $265.80   $265.80  
  Purchase #3 $112.35   6.672%   $119.846   $119.85   $119.85   $119.80  
  Purchase #4 $15.84   10.190%   $17.4541   $17.45   $17.45   $17.50  
  Purchase #5 $56.30   6.300%   $59.8469   $59.85   $59.85   $59.80  
  Purchase #6 $33.58   7.631%   $36.1425   $36.14   $36.15   $36.10  
  Purchase #7 $113.76   7.561%   $122.3614   $122.36   $122.35   $122.40  
  7 purchase totals = $694.69       $748.0086   $748.01   $748.00   $748.00