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 $164.51   8.496%   $178.4868   $178.49   $178.50   $178.50  
  Purchase #2 $127.55   10.272%   $140.6519   $140.65   $140.65   $140.70  
  Purchase #3 $182.42   8.871%   $198.6025   $198.60   $198.60   $198.60  
  Purchase #4 $24.82   7.454%   $26.6701   $26.67   $26.65   $26.70  
  Purchase #5 $247.66   10.343%   $273.2755   $273.28   $273.30   $273.30  
  Purchase #6 $159.60   13.157%   $180.5986   $180.60   $180.60   $180.60  
  Purchase #7 $42.30   3.155%   $43.6346   $43.63   $43.65   $43.60  
  7 purchase totals = $948.86       $1,041.9200   $1,041.92   $1,041.95   $1,042.00