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 $229.36   7.535%   $246.6423   $246.64   $246.65   $246.60  
  Purchase #2 $110.84   5.241%   $116.6491   $116.65   $116.65   $116.60  
  Purchase #3 $175.58   6.493%   $186.9804   $186.98   $187.00   $187.00  
  Purchase #4 $59.45   6.201%   $63.1365   $63.14   $63.15   $63.10  
  Purchase #5 $31.78   4.642%   $33.2552   $33.26   $33.25   $33.30  
  Purchase #6 $96.32   12.595%   $108.4515   $108.45   $108.45   $108.50  
  Purchase #7 $131.64   4.744%   $137.885   $137.89   $137.90   $137.90  
  7 purchase totals = $834.97       $893.0000   $893.01   $893.05   $893.00