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 $77.69   11.112%   $86.3229   $86.32   $86.30   $86.30  
  Purchase #2 $88.28   8.770%   $96.0222   $96.02   $96.00   $96.00  
  Purchase #3 $167.98   4.496%   $175.5324   $175.53   $175.55   $175.50  
  Purchase #4 $236.91   9.807%   $260.1438   $260.14   $260.15   $260.10  
  Purchase #5 $105.83   6.816%   $113.0434   $113.04   $113.05   $113.00  
  Purchase #6 $65.71   7.244%   $70.47   $70.47   $70.45   $70.50  
  Purchase #7 $87.63   5.122%   $92.1184   $92.12   $92.10   $92.10  
  7 purchase totals = $830.03       $893.6531   $893.64   $893.60   $893.50