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 $87.57   6.546%   $93.3023   $93.30   $93.30   $93.30  
  Purchase #2 $177.54   10.260%   $195.7556   $195.76   $195.75   $195.80  
  Purchase #3 $127.57   10.503%   $140.9687   $140.97   $140.95   $141.00  
  Purchase #4 $107.85   4.530%   $112.7356   $112.74   $112.75   $112.70  
  Purchase #5 $76.26   12.276%   $85.6217   $85.62   $85.60   $85.60  
  Purchase #6 $64.95   12.705%   $73.2019   $73.20   $73.20   $73.20  
  Purchase #7 $169.84   10.314%   $187.3573   $187.36   $187.35   $187.40  
  7 purchase totals = $811.58       $888.9431   $888.95   $888.90   $889.00