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 $210.82   3.810%   $218.8522   $218.85   $218.85   $218.90  
  Purchase #2 $73.76   13.266%   $83.545   $83.55   $83.55   $83.50  
  Purchase #3 $112.47   9.303%   $122.9331   $122.93   $122.95   $122.90  
  Purchase #4 $210.64   11.523%   $234.912   $234.91   $234.90   $234.90  
  Purchase #5 $237.75   6.307%   $252.7449   $252.74   $252.75   $252.70  
  Purchase #6 $153.83   10.246%   $169.5914   $169.59   $169.60   $169.60  
  Purchase #7 $108.95   9.137%   $118.9048   $118.90   $118.90   $118.90  
  7 purchase totals = $1,108.22       $1,201.4834   $1,201.47   $1,201.50   $1,201.40