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 $102.85   13.260%   $116.4879   $116.49   $116.50   $116.50  
  Purchase #2 $181.38   6.759%   $193.6395   $193.64   $193.65   $193.60  
  Purchase #3 $172.57   4.119%   $179.6782   $179.68   $179.70   $179.70  
  Purchase #4 $117.62   13.306%   $133.2705   $133.27   $133.25   $133.30  
  Purchase #5 $241.91   6.604%   $257.8857   $257.89   $257.90   $257.90  
  Purchase #6 $165.82   4.308%   $172.9635   $172.96   $172.95   $173.00  
  Purchase #7 $203.68   5.754%   $215.3997   $215.40   $215.40   $215.40  
  7 purchase totals = $1,185.83       $1,269.3250   $1,269.33   $1,269.35   $1,269.40