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 $162.62   8.136%   $175.8508   $175.85   $175.85   $175.90  
  Purchase #2 $111.95   11.535%   $124.8634   $124.86   $124.85   $124.90  
  Purchase #3 $122.57   11.346%   $136.4768   $136.48   $136.50   $136.50  
  Purchase #4 $28.44   7.534%   $30.5827   $30.58   $30.60   $30.60  
  Purchase #5 $192.59   6.121%   $204.3784   $204.38   $204.40   $204.40  
  Purchase #6 $24.89   10.646%   $27.5398   $27.54   $27.55   $27.50  
  Purchase #7 $56.36   7.112%   $60.3683   $60.37   $60.35   $60.40  
  7 purchase totals = $699.42       $760.0602   $760.06   $760.10   $760.20