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 $87.69   6.729%   $93.5907   $93.59   $93.60   $93.60  
  Purchase #2 $243.49   9.366%   $266.2953   $266.30   $266.30   $266.30  
  Purchase #3 $82.47   8.585%   $89.55   $89.55   $89.55   $89.60  
  Purchase #4 $93.62   3.717%   $97.0999   $97.10   $97.10   $97.10  
  Purchase #5 $236.85   4.817%   $248.2591   $248.26   $248.25   $248.30  
  Purchase #6 $188.37   13.475%   $213.7529   $213.75   $213.75   $213.80  
  Purchase #7 $61.26   10.264%   $67.5477   $67.55   $67.55   $67.50  
  7 purchase totals = $993.75       $1,076.0956   $1,076.10   $1,076.10   $1,076.20