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 $167.79   11.242%   $186.653   $186.65   $186.65   $186.70  
  Purchase #2 $30.82   11.614%   $34.3994   $34.40   $34.40   $34.40  
  Purchase #3 $24.97   6.577%   $26.6123   $26.61   $26.60   $26.60  
  Purchase #4 $60.54   13.245%   $68.5585   $68.56   $68.55   $68.60  
  Purchase #5 $187.58   11.391%   $208.9472   $208.95   $208.95   $208.90  
  Purchase #6 $178.58   9.672%   $195.8523   $195.85   $195.85   $195.90  
  Purchase #7 $33.59   13.541%   $38.1384   $38.14   $38.15   $38.10  
  7 purchase totals = $683.87       $759.1611   $759.16   $759.15   $759.20