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 $222.97   10.696%   $246.8189   $246.82   $246.80   $246.80  
  Purchase #2 $111.95   7.537%   $120.3877   $120.39   $120.40   $120.40  
  Purchase #3 $32.68   11.282%   $36.367   $36.37   $36.35   $36.40  
  Purchase #4 $23.91   3.385%   $24.7194   $24.72   $24.70   $24.70  
  Purchase #5 $65.59   12.794%   $73.9816   $73.98   $74.00   $74.00  
  Purchase #6 $206.68   5.389%   $217.818   $217.82   $217.80   $217.80  
  Purchase #7 $165.34   12.536%   $186.067   $186.07   $186.05   $186.10  
  7 purchase totals = $829.12       $906.1596   $906.17   $906.10   $906.20