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 $55.38   8.148%   $59.8924   $59.89   $59.90   $59.90  
  Purchase #2 $106.95   10.301%   $117.9669   $117.97   $117.95   $118.00  
  Purchase #3 $234.95   4.770%   $246.1571   $246.16   $246.15   $246.20  
  Purchase #4 $33.66   5.457%   $35.4968   $35.50   $35.50   $35.50  
  Purchase #5 $239.76   7.254%   $257.1522   $257.15   $257.15   $257.20  
  Purchase #6 $142.66   3.559%   $147.7373   $147.74   $147.75   $147.70  
  Purchase #7 $187.77   4.497%   $196.214   $196.21   $196.20   $196.20  
  7 purchase totals = $1,001.13       $1,060.6167   $1,060.62   $1,060.60   $1,060.70