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 $35.91   8.114%   $38.8237   $38.82   $38.80   $38.80  
  Purchase #2 $213.38   10.268%   $235.2899   $235.29   $235.30   $235.30  
  Purchase #3 $238.75   3.264%   $246.5428   $246.54   $246.55   $246.50  
  Purchase #4 $86.54   8.158%   $93.5999   $93.60   $93.60   $93.60  
  Purchase #5 $183.57   12.684%   $206.854   $206.85   $206.85   $206.90  
  Purchase #6 $21.86   9.615%   $23.9618   $23.96   $23.95   $24.00  
  Purchase #7 $125.94   4.515%   $131.6262   $131.63   $131.65   $131.60  
  7 purchase totals = $905.95       $976.6983   $976.69   $976.70   $976.70