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 $247.55   7.304%   $265.6311   $265.63   $265.65   $265.60  
  Purchase #2 $227.94   7.768%   $245.6464   $245.65   $245.65   $245.60  
  Purchase #3 $206.36   11.435%   $229.9573   $229.96   $229.95   $230.00  
  Purchase #4 $222.94   4.759%   $233.5497   $233.55   $233.55   $233.50  
  Purchase #5 $250.89   13.395%   $284.4967   $284.50   $284.50   $284.50  
  Purchase #6 $29.51   10.801%   $32.6974   $32.70   $32.70   $32.70  
  Purchase #7 $70.98   5.521%   $74.8988   $74.90   $74.90   $74.90  
  7 purchase totals = $1,256.17       $1,366.8774   $1,366.89   $1,366.90   $1,366.80