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 $239.25   3.211%   $246.9323   $246.93   $246.95   $246.90  
  Purchase #2 $109.26   12.286%   $122.6837   $122.68   $122.70   $122.70  
  Purchase #3 $92.54   9.739%   $101.5525   $101.55   $101.55   $101.60  
  Purchase #4 $206.43   3.207%   $213.0502   $213.05   $213.05   $213.10  
  Purchase #5 $70.62   10.390%   $77.9574   $77.96   $77.95   $78.00  
  Purchase #6 $61.54   3.211%   $63.516   $63.52   $63.50   $63.50  
  Purchase #7 $66.58   12.146%   $74.6668   $74.67   $74.65   $74.70  
  7 purchase totals = $846.22       $900.3589   $900.36   $900.35   $900.50