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 $174.55   9.374%   $190.9123   $190.91   $190.90   $190.90  
  Purchase #2 $133.26   11.551%   $148.6529   $148.65   $148.65   $148.70  
  Purchase #3 $247.62   4.347%   $258.384   $258.38   $258.40   $258.40  
  Purchase #4 $64.65   6.373%   $68.7701   $68.77   $68.75   $68.80  
  Purchase #5 $16.34   13.509%   $18.5474   $18.55   $18.55   $18.50  
  Purchase #6 $153.95   9.771%   $168.9925   $168.99   $169.00   $169.00  
  Purchase #7 $195.91   6.147%   $207.9526   $207.95   $207.95   $208.00  
  7 purchase totals = $986.28       $1,062.2118   $1,062.20   $1,062.20   $1,062.30