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 $208.33   12.653%   $234.69   $234.69   $234.70   $234.70  
  Purchase #2 $9.60   13.374%   $10.8839   $10.88   $10.90   $10.90  
  Purchase #3 $61.36   7.106%   $65.7202   $65.72   $65.70   $65.70  
  Purchase #4 $147.81   5.216%   $155.5198   $155.52   $155.50   $155.50  
  Purchase #5 $213.84   9.343%   $233.8191   $233.82   $233.80   $233.80  
  Purchase #6 $120.55   11.503%   $134.4169   $134.42   $134.40   $134.40  
  Purchase #7 $193.88   9.260%   $211.8333   $211.83   $211.85   $211.80  
  7 purchase totals = $955.37       $1,046.8832   $1,046.88   $1,046.85   $1,046.80