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 $54.76   12.654%   $61.6893   $61.69   $61.70   $61.70  
  Purchase #2 $71.84   9.453%   $78.631   $78.63   $78.65   $78.60  
  Purchase #3 $28.46   5.705%   $30.0836   $30.08   $30.10   $30.10  
  Purchase #4 $94.39   9.221%   $103.0937   $103.09   $103.10   $103.10  
  Purchase #5 $50.79   8.706%   $55.2118   $55.21   $55.20   $55.20  
  Purchase #6 $120.84   6.356%   $128.5206   $128.52   $128.50   $128.50  
  Purchase #7 $26.73   10.482%   $29.5318   $29.53   $29.55   $29.50  
  7 purchase totals = $447.81       $486.7618   $486.75   $486.80   $486.70