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 $66.36   6.741%   $70.8333   $70.83   $70.85   $70.80  
  Purchase #2 $192.41   10.413%   $212.4457   $212.45   $212.45   $212.40  
  Purchase #3 $63.85   12.846%   $72.0522   $72.05   $72.05   $72.10  
  Purchase #4 $123.28   5.669%   $130.2687   $130.27   $130.25   $130.30  
  Purchase #5 $241.27   10.666%   $267.0039   $267.00   $267.00   $267.00  
  Purchase #6 $84.76   11.785%   $94.749   $94.75   $94.75   $94.70  
  Purchase #7 $90.65   7.414%   $97.3708   $97.37   $97.35   $97.40  
  7 purchase totals = $862.58       $944.7236   $944.72   $944.70   $944.70