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 $156.32   6.483%   $166.4542   $166.45   $166.45   $166.50  
  Purchase #2 $58.63   5.188%   $61.6717   $61.67   $61.65   $61.70  
  Purchase #3 $87.84   9.522%   $96.2041   $96.20   $96.20   $96.20  
  Purchase #4 $81.57   6.160%   $86.5947   $86.59   $86.60   $86.60  
  Purchase #5 $113.66   7.445%   $122.122   $122.12   $122.10   $122.10  
  Purchase #6 $213.55   11.834%   $238.8215   $238.82   $238.80   $238.80  
  Purchase #7 $55.45   8.225%   $60.0108   $60.01   $60.00   $60.00  
  7 purchase totals = $767.02       $831.8790   $831.86   $831.80   $831.90