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 $68.54   6.601%   $73.0643   $73.06   $73.05   $73.10  
  Purchase #2 $131.76   3.119%   $135.8696   $135.87   $135.85   $135.90  
  Purchase #3 $145.75   11.547%   $162.5798   $162.58   $162.60   $162.60  
  Purchase #4 $26.43   4.866%   $27.7161   $27.72   $27.70   $27.70  
  Purchase #5 $226.37   12.451%   $254.5553   $254.56   $254.55   $254.60  
  Purchase #6 $206.36   6.340%   $219.4432   $219.44   $219.45   $219.40  
  Purchase #7 $97.72   7.780%   $105.3226   $105.32   $105.30   $105.30  
  7 purchase totals = $902.93       $978.5509   $978.55   $978.50   $978.60