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 $214.87   9.649%   $235.6028   $235.60   $235.60   $235.60  
  Purchase #2 $217.94   7.800%   $234.9393   $234.94   $234.95   $234.90  
  Purchase #3 $75.28   10.237%   $82.9864   $82.99   $83.00   $83.00  
  Purchase #4 $136.62   4.380%   $142.604   $142.60   $142.60   $142.60  
  Purchase #5 $7.97   7.847%   $8.5954   $8.60   $8.60   $8.60  
  Purchase #6 $60.80   4.558%   $63.5713   $63.57   $63.55   $63.60  
  Purchase #7 $130.52   12.405%   $146.711   $146.71   $146.70   $146.70  
  7 purchase totals = $844.00       $915.0102   $915.01   $915.00   $915.00