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 $52.36   7.246%   $56.154   $56.15   $56.15   $56.20  
  Purchase #2 $82.51   7.404%   $88.619   $88.62   $88.60   $88.60  
  Purchase #3 $86.31   11.221%   $95.9948   $95.99   $96.00   $96.00  
  Purchase #4 $58.80   3.694%   $60.9721   $60.97   $60.95   $61.00  
  Purchase #5 $158.86   8.827%   $172.8826   $172.88   $172.90   $172.90  
  Purchase #6 $215.51   6.348%   $229.1906   $229.19   $229.20   $229.20  
  Purchase #7 $138.64   13.380%   $157.19   $157.19   $157.20   $157.20  
  7 purchase totals = $792.99       $861.0031   $860.99   $861.00   $861.10