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 $38.35   6.212%   $40.7323   $40.73   $40.75   $40.70  
  Purchase #2 $247.44   11.496%   $275.8857   $275.89   $275.90   $275.90  
  Purchase #3 $237.71   9.623%   $260.5848   $260.58   $260.60   $260.60  
  Purchase #4 $198.55   13.737%   $225.8248   $225.82   $225.80   $225.80  
  Purchase #5 $103.41   4.787%   $108.3602   $108.36   $108.35   $108.40  
  Purchase #6 $236.61   4.862%   $248.114   $248.11   $248.10   $248.10  
  Purchase #7 $13.41   9.683%   $14.7085   $14.71   $14.70   $14.70  
  7 purchase totals = $1,075.48       $1,174.2103   $1,174.20   $1,174.20   $1,174.20