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 $56.69   12.272%   $63.647   $63.65   $63.65   $63.60  
  Purchase #2 $79.70   5.252%   $83.8858   $83.89   $83.90   $83.90  
  Purchase #3 $17.36   12.720%   $19.5682   $19.57   $19.55   $19.60  
  Purchase #4 $235.62   4.701%   $246.6965   $246.70   $246.70   $246.70  
  Purchase #5 $16.43   8.782%   $17.8729   $17.87   $17.85   $17.90  
  Purchase #6 $92.39   9.381%   $101.0571   $101.06   $101.05   $101.10  
  Purchase #7 $228.72   4.284%   $238.5184   $238.52   $238.50   $238.50  
  7 purchase totals = $726.91       $771.2459   $771.26   $771.20   $771.30