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 $179.52   13.113%   $203.0605   $203.06   $203.05   $203.10  
  Purchase #2 $246.59   12.367%   $277.0858   $277.09   $277.10   $277.10  
  Purchase #3 $63.27   11.207%   $70.3607   $70.36   $70.35   $70.40  
  Purchase #4 $216.49   3.417%   $223.8875   $223.89   $223.90   $223.90  
  Purchase #5 $248.76   3.571%   $257.6432   $257.64   $257.65   $257.60  
  Purchase #6 $40.28   8.777%   $43.8154   $43.82   $43.80   $43.80  
  Purchase #7 $227.41   8.688%   $247.1674   $247.17   $247.15   $247.20  
  7 purchase totals = $1,222.32       $1,323.0205   $1,323.03   $1,323.00   $1,323.10