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 $10.42   13.743%   $11.852   $11.85   $11.85   $11.90  
  Purchase #2 $226.49   12.741%   $255.3471   $255.35   $255.35   $255.30  
  Purchase #3 $242.58   11.743%   $271.0662   $271.07   $271.05   $271.10  
  Purchase #4 $37.46   5.670%   $39.584   $39.58   $39.60   $39.60  
  Purchase #5 $165.69   8.159%   $179.2086   $179.21   $179.20   $179.20  
  Purchase #6 $23.78   9.567%   $26.055   $26.06   $26.05   $26.10  
  Purchase #7 $163.50   5.555%   $172.5824   $172.58   $172.60   $172.60  
  7 purchase totals = $869.92       $955.6953   $955.70   $955.70   $955.80