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 $168.96   8.517%   $183.3503   $183.35   $183.35   $183.40  
  Purchase #2 $153.91   8.452%   $166.9185   $166.92   $166.90   $166.90  
  Purchase #3 $241.97   5.146%   $254.4218   $254.42   $254.40   $254.40  
  Purchase #4 $151.30   9.418%   $165.5494   $165.55   $165.55   $165.50  
  Purchase #5 $64.97   8.747%   $70.6529   $70.65   $70.65   $70.70  
  Purchase #6 $64.76   4.109%   $67.421   $67.42   $67.40   $67.40  
  Purchase #7 $184.35   5.777%   $194.9999   $195.00   $195.00   $195.00  
  7 purchase totals = $1,030.22       $1,103.3138   $1,103.31   $1,103.25   $1,103.30