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 $56.99   12.826%   $64.2995   $64.30   $64.30   $64.30  
  Purchase #2 $142.77   3.379%   $147.5942   $147.59   $147.60   $147.60  
  Purchase #3 $63.30   11.526%   $70.596   $70.60   $70.60   $70.60  
  Purchase #4 $145.79   6.128%   $154.724   $154.72   $154.70   $154.70  
  Purchase #5 $196.82   5.129%   $206.9149   $206.91   $206.90   $206.90  
  Purchase #6 $158.28   5.356%   $166.7575   $166.76   $166.75   $166.80  
  Purchase #7 $203.78   12.530%   $229.3136   $229.31   $229.30   $229.30  
  7 purchase totals = $967.73       $1,040.1997   $1,040.19   $1,040.15   $1,040.20