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 $177.43   13.638%   $201.6279   $201.63   $201.65   $201.60  
  Purchase #2 $108.47   8.328%   $117.5034   $117.50   $117.50   $117.50  
  Purchase #3 $98.33   5.619%   $103.8552   $103.86   $103.85   $103.90  
  Purchase #4 $116.40   10.318%   $128.4102   $128.41   $128.40   $128.40  
  Purchase #5 $176.64   11.729%   $197.3581   $197.36   $197.35   $197.40  
  Purchase #6 $224.52   11.352%   $250.0075   $250.01   $250.00   $250.00  
  Purchase #7 $79.76   9.307%   $87.1833   $87.18   $87.20   $87.20  
  7 purchase totals = $981.55       $1,085.9456   $1,085.95   $1,085.95   $1,086.00