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 $88.98   8.361%   $96.4196   $96.42   $96.40   $96.40  
  Purchase #2 $58.34   12.596%   $65.6885   $65.69   $65.70   $65.70  
  Purchase #3 $127.30   8.326%   $137.899   $137.90   $137.90   $137.90  
  Purchase #4 $159.86   9.110%   $174.4232   $174.42   $174.40   $174.40  
  Purchase #5 $60.44   10.168%   $66.5855   $66.59   $66.60   $66.60  
  Purchase #6 $203.69   7.832%   $219.643   $219.64   $219.65   $219.60  
  Purchase #7 $125.45   3.765%   $130.1732   $130.17   $130.15   $130.20  
  7 purchase totals = $824.06       $890.8320   $890.83   $890.80   $890.80