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 $118.64   4.424%   $123.8886   $123.89   $123.90   $123.90  
  Purchase #2 $212.49   11.393%   $236.699   $236.70   $236.70   $236.70  
  Purchase #3 $206.56   3.825%   $214.4609   $214.46   $214.45   $214.50  
  Purchase #4 $64.87   5.251%   $68.2763   $68.28   $68.30   $68.30  
  Purchase #5 $107.55   6.803%   $114.8666   $114.87   $114.85   $114.90  
  Purchase #6 $14.50   13.279%   $16.4255   $16.43   $16.45   $16.40  
  Purchase #7 $246.40   7.161%   $264.0447   $264.04   $264.05   $264.00  
  7 purchase totals = $971.01       $1,038.6616   $1,038.67   $1,038.70   $1,038.70