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 $39.42   12.320%   $44.2765   $44.28   $44.30   $44.30  
  Purchase #2 $61.46   8.309%   $66.5667   $66.57   $66.55   $66.60  
  Purchase #3 $205.83   12.743%   $232.0589   $232.06   $232.05   $232.10  
  Purchase #4 $188.98   13.640%   $214.7569   $214.76   $214.75   $214.80  
  Purchase #5 $203.27   4.246%   $211.9008   $211.90   $211.90   $211.90  
  Purchase #6 $48.66   6.820%   $51.9786   $51.98   $52.00   $52.00  
  Purchase #7 $118.92   6.212%   $126.3073   $126.31   $126.30   $126.30  
  7 purchase totals = $866.54       $947.8457   $947.86   $947.85   $948.00