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 $193.67   6.696%   $206.6381   $206.64   $206.65   $206.60  
  Purchase #2 $71.78   6.649%   $76.5527   $76.55   $76.55   $76.60  
  Purchase #3 $125.29   8.524%   $135.9697   $135.97   $135.95   $136.00  
  Purchase #4 $157.84   7.362%   $169.4602   $169.46   $169.45   $169.50  
  Purchase #5 $168.62   11.454%   $187.9337   $187.93   $187.95   $187.90  
  Purchase #6 $250.32   7.156%   $268.2329   $268.23   $268.25   $268.20  
  Purchase #7 $16.88   3.207%   $17.4213   $17.42   $17.40   $17.40  
  7 purchase totals = $984.40       $1,062.2086   $1,062.20   $1,062.20   $1,062.20