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 $54.88   12.763%   $61.8843   $61.88   $61.90   $61.90  
  Purchase #2 $203.70   6.291%   $216.5148   $216.51   $216.50   $216.50  
  Purchase #3 $190.81   13.109%   $215.8233   $215.82   $215.80   $215.80  
  Purchase #4 $237.41   11.284%   $264.1993   $264.20   $264.20   $264.20  
  Purchase #5 $117.88   9.712%   $129.3285   $129.33   $129.35   $129.30  
  Purchase #6 $247.44   8.146%   $267.5965   $267.60   $267.60   $267.60  
  Purchase #7 $175.69   6.233%   $186.6408   $186.64   $186.65   $186.60  
  7 purchase totals = $1,227.81       $1,341.9875   $1,341.98   $1,342.00   $1,341.90