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 $43.58   10.720%   $48.2518   $48.25   $48.25   $48.30  
  Purchase #2 $222.92   11.399%   $248.3307   $248.33   $248.35   $248.30  
  Purchase #3 $248.89   4.168%   $259.2637   $259.26   $259.25   $259.30  
  Purchase #4 $109.49   10.749%   $121.2591   $121.26   $121.25   $121.30  
  Purchase #5 $76.74   5.243%   $80.7635   $80.76   $80.75   $80.80  
  Purchase #6 $225.72   10.399%   $249.1926   $249.19   $249.20   $249.20  
  Purchase #7 $151.74   7.265%   $162.7639   $162.76   $162.75   $162.80  
  7 purchase totals = $1,079.08       $1,169.8253   $1,169.81   $1,169.80   $1,170.00