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 $192.29   8.137%   $207.9366   $207.94   $207.95   $207.90  
  Purchase #2 $24.70   3.510%   $25.567   $25.57   $25.55   $25.60  
  Purchase #3 $63.68   4.813%   $66.7449   $66.74   $66.75   $66.70  
  Purchase #4 $80.55   11.219%   $89.5869   $89.59   $89.60   $89.60  
  Purchase #5 $105.50   9.224%   $115.2313   $115.23   $115.25   $115.20  
  Purchase #6 $57.29   8.409%   $62.1075   $62.11   $62.10   $62.10  
  Purchase #7 $54.94   13.666%   $62.4481   $62.45   $62.45   $62.40  
  7 purchase totals = $578.95       $629.6223   $629.63   $629.65   $629.50