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 $61.98   11.755%   $69.2657   $69.27   $69.25   $69.30  
  Purchase #2 $201.75   10.655%   $223.2465   $223.25   $223.25   $223.20  
  Purchase #3 $214.98   4.476%   $224.6025   $224.60   $224.60   $224.60  
  Purchase #4 $175.84   8.849%   $191.4001   $191.40   $191.40   $191.40  
  Purchase #5 $143.29   8.705%   $155.7634   $155.76   $155.75   $155.80  
  Purchase #6 $35.94   4.556%   $37.5774   $37.58   $37.60   $37.60  
  Purchase #7 $64.65   9.121%   $70.5467   $70.55   $70.55   $70.50  
  7 purchase totals = $898.43       $972.4023   $972.41   $972.40   $972.40