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 $152.65   8.102%   $165.0177   $165.02   $165.00   $165.00  
  Purchase #2 $124.49   4.703%   $130.3448   $130.34   $130.35   $130.30  
  Purchase #3 $236.86   11.652%   $264.4589   $264.46   $264.45   $264.50  
  Purchase #4 $184.74   7.727%   $199.0149   $199.01   $199.00   $199.00  
  Purchase #5 $15.47   6.672%   $16.5022   $16.50   $16.50   $16.50  
  Purchase #6 $134.91   10.176%   $148.6384   $148.64   $148.65   $148.60  
  Purchase #7 $135.49   11.682%   $151.3179   $151.32   $151.30   $151.30  
  7 purchase totals = $984.61       $1,075.2948   $1,075.29   $1,075.25   $1,075.20