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 $243.98   8.693%   $265.1892   $265.19   $265.20   $265.20  
  Purchase #2 $221.65   8.403%   $240.2752   $240.28   $240.30   $240.30  
  Purchase #3 $146.89   13.383%   $166.5483   $166.55   $166.55   $166.50  
  Purchase #4 $192.85   9.446%   $211.0666   $211.07   $211.05   $211.10  
  Purchase #5 $87.47   5.755%   $92.5039   $92.50   $92.50   $92.50  
  Purchase #6 $9.32   13.192%   $10.5495   $10.55   $10.55   $10.50  
  Purchase #7 $168.89   4.252%   $176.0712   $176.07   $176.05   $176.10  
  7 purchase totals = $1,071.05       $1,162.2039   $1,162.21   $1,162.20   $1,162.20