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 $197.93   13.161%   $223.9796   $223.98   $224.00   $224.00  
  Purchase #2 $102.58   10.552%   $113.4042   $113.40   $113.40   $113.40  
  Purchase #3 $154.64   11.637%   $172.6355   $172.64   $172.65   $172.60  
  Purchase #4 $13.51   7.656%   $14.5443   $14.54   $14.55   $14.50  
  Purchase #5 $242.98   8.703%   $264.1265   $264.13   $264.15   $264.10  
  Purchase #6 $214.65   11.210%   $238.7123   $238.71   $238.70   $238.70  
  Purchase #7 $32.64   8.599%   $35.4467   $35.45   $35.45   $35.40  
  7 purchase totals = $958.93       $1,062.8491   $1,062.85   $1,062.90   $1,062.70