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 $68.58   12.553%   $77.1888   $77.19   $77.20   $77.20  
  Purchase #2 $42.32   9.643%   $46.4009   $46.40   $46.40   $46.40  
  Purchase #3 $194.79   12.549%   $219.2342   $219.23   $219.25   $219.20  
  Purchase #4 $218.43   9.676%   $239.5653   $239.57   $239.55   $239.60  
  Purchase #5 $61.27   6.127%   $65.024   $65.02   $65.00   $65.00  
  Purchase #6 $124.60   11.135%   $138.4742   $138.47   $138.45   $138.50  
  Purchase #7 $174.60   6.743%   $186.3733   $186.37   $186.35   $186.40  
  7 purchase totals = $884.59       $972.2607   $972.25   $972.20   $972.30