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 $171.92   8.483%   $186.504   $186.50   $186.50   $186.50  
  Purchase #2 $182.25   8.158%   $197.118   $197.12   $197.10   $197.10  
  Purchase #3 $68.29   6.258%   $72.5636   $72.56   $72.55   $72.60  
  Purchase #4 $98.78   6.426%   $105.1276   $105.13   $105.15   $105.10  
  Purchase #5 $216.69   8.651%   $235.4359   $235.44   $235.45   $235.40  
  Purchase #6 $184.64   6.654%   $196.9259   $196.93   $196.95   $196.90  
  Purchase #7 $236.77   6.104%   $251.2224   $251.22   $251.20   $251.20  
  7 purchase totals = $1,159.34       $1,244.8974   $1,244.90   $1,244.90   $1,244.80