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 $233.78   13.861%   $266.1842   $266.18   $266.20   $266.20  
  Purchase #2 $55.73   12.405%   $62.6433   $62.64   $62.65   $62.60  
  Purchase #3 $46.98   11.580%   $52.4203   $52.42   $52.40   $52.40  
  Purchase #4 $188.58   7.692%   $203.0856   $203.09   $203.10   $203.10  
  Purchase #5 $30.25   9.677%   $33.1773   $33.18   $33.20   $33.20  
  Purchase #6 $177.70   11.552%   $198.2279   $198.23   $198.25   $198.20  
  Purchase #7 $53.95   11.584%   $60.1996   $60.20   $60.20   $60.20  
  7 purchase totals = $786.97       $875.9382   $875.94   $876.00   $875.90