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 $163.54   11.869%   $182.9506   $182.95   $182.95   $183.00  
  Purchase #2 $225.57   7.476%   $242.4336   $242.43   $242.45   $242.40  
  Purchase #3 $162.96   5.866%   $172.5192   $172.52   $172.50   $172.50  
  Purchase #4 $221.83   8.412%   $240.4903   $240.49   $240.50   $240.50  
  Purchase #5 $187.75   10.446%   $207.3624   $207.36   $207.35   $207.40  
  Purchase #6 $5.54   8.360%   $6.0031   $6.00   $6.00   $6.00  
  Purchase #7 $203.83   10.156%   $224.531   $224.53   $224.55   $224.50  
  7 purchase totals = $1,171.02       $1,276.2902   $1,276.28   $1,276.30   $1,276.30