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 $92.53   3.827%   $96.0711   $96.07   $96.05   $96.10  
  Purchase #2 $23.83   11.295%   $26.5216   $26.52   $26.50   $26.50  
  Purchase #3 $17.59   12.603%   $19.8069   $19.81   $19.80   $19.80  
  Purchase #4 $214.26   8.301%   $232.0457   $232.05   $232.05   $232.00  
  Purchase #5 $134.69   11.156%   $149.716   $149.72   $149.70   $149.70  
  Purchase #6 $117.82   6.808%   $125.8412   $125.84   $125.85   $125.80  
  Purchase #7 $142.33   10.444%   $157.1949   $157.19   $157.20   $157.20  
  7 purchase totals = $743.05       $807.1974   $807.20   $807.15   $807.10