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 $234.65   11.505%   $261.6465   $261.65   $261.65   $261.60  
  Purchase #2 $183.81   12.103%   $206.0565   $206.06   $206.05   $206.10  
  Purchase #3 $178.99   7.557%   $192.5163   $192.52   $192.50   $192.50  
  Purchase #4 $21.33   12.849%   $24.0707   $24.07   $24.05   $24.10  
  Purchase #5 $98.67   4.487%   $103.0973   $103.10   $103.10   $103.10  
  Purchase #6 $242.53   13.795%   $275.987   $275.99   $276.00   $276.00  
  Purchase #7 $35.84   8.167%   $38.7671   $38.77   $38.75   $38.80  
  7 purchase totals = $995.82       $1,102.1414   $1,102.16   $1,102.10   $1,102.20