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 $181.81   13.171%   $205.7562   $205.76   $205.75   $205.80  
  Purchase #2 $136.26   3.159%   $140.5645   $140.56   $140.55   $140.60  
  Purchase #3 $24.33   10.740%   $26.943   $26.94   $26.95   $26.90  
  Purchase #4 $87.77   10.538%   $97.0192   $97.02   $97.00   $97.00  
  Purchase #5 $69.91   13.801%   $79.5583   $79.56   $79.55   $79.60  
  Purchase #6 $201.56   8.802%   $219.3013   $219.30   $219.30   $219.30  
  Purchase #7 $52.58   13.128%   $59.4827   $59.48   $59.50   $59.50  
  7 purchase totals = $754.22       $828.6252   $828.62   $828.60   $828.70