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 $223.66   13.873%   $254.6884   $254.69   $254.70   $254.70  
  Purchase #2 $29.89   9.320%   $32.6757   $32.68   $32.70   $32.70  
  Purchase #3 $167.36   10.285%   $184.573   $184.57   $184.55   $184.60  
  Purchase #4 $198.71   10.211%   $219.0003   $219.00   $219.00   $219.00  
  Purchase #5 $18.47   3.660%   $19.146   $19.15   $19.15   $19.10  
  Purchase #6 $86.62   11.190%   $96.3128   $96.31   $96.30   $96.30  
  Purchase #7 $34.88   6.273%   $37.068   $37.07   $37.05   $37.10  
  7 purchase totals = $759.59       $843.4642   $843.47   $843.45   $843.50