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 $62.69   9.727%   $68.7879   $68.79   $68.80   $68.80  
  Purchase #2 $117.70   6.188%   $124.9833   $124.98   $125.00   $125.00  
  Purchase #3 $213.48   9.629%   $234.036   $234.04   $234.05   $234.00  
  Purchase #4 $18.59   13.726%   $21.1417   $21.14   $21.15   $21.10  
  Purchase #5 $79.70   9.599%   $87.3504   $87.35   $87.35   $87.40  
  Purchase #6 $181.27   11.643%   $202.3753   $202.38   $202.40   $202.40  
  Purchase #7 $122.64   10.670%   $135.7257   $135.73   $135.75   $135.70  
  7 purchase totals = $796.07       $874.4003   $874.41   $874.50   $874.40