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 $179.35   12.769%   $202.2512   $202.25   $202.25   $202.30  
  Purchase #2 $81.74   8.368%   $88.58   $88.58   $88.60   $88.60  
  Purchase #3 $211.75   13.245%   $239.7963   $239.80   $239.80   $239.80  
  Purchase #4 $81.67   6.842%   $87.2579   $87.26   $87.25   $87.30  
  Purchase #5 $15.61   13.450%   $17.7095   $17.71   $17.70   $17.70  
  Purchase #6 $112.69   3.278%   $116.384   $116.38   $116.40   $116.40  
  Purchase #7 $231.71   7.437%   $248.9423   $248.94   $248.95   $248.90  
  7 purchase totals = $914.52       $1,000.9212   $1,000.92   $1,000.95   $1,001.00