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 $32.34   3.781%   $33.5628   $33.56   $33.55   $33.60  
  Purchase #2 $246.52   6.381%   $262.2504   $262.25   $262.25   $262.30  
  Purchase #3 $188.44   6.697%   $201.0598   $201.06   $201.05   $201.10  
  Purchase #4 $154.49   11.516%   $172.2811   $172.28   $172.30   $172.30  
  Purchase #5 $70.37   6.852%   $75.1918   $75.19   $75.20   $75.20  
  Purchase #6 $11.69   6.619%   $12.4638   $12.46   $12.45   $12.50  
  Purchase #7 $242.29   8.478%   $262.8313   $262.83   $262.85   $262.80  
  7 purchase totals = $946.14       $1,019.6410   $1,019.63   $1,019.65   $1,019.80