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 $63.98   7.787%   $68.9621   $68.96   $68.95   $69.00  
  Purchase #2 $47.47   4.450%   $49.5824   $49.58   $49.60   $49.60  
  Purchase #3 $83.26   5.794%   $88.0841   $88.08   $88.10   $88.10  
  Purchase #4 $73.89   6.407%   $78.6241   $78.62   $78.60   $78.60  
  Purchase #5 $11.50   6.166%   $12.2091   $12.21   $12.20   $12.20  
  Purchase #6 $205.32   10.837%   $227.5705   $227.57   $227.55   $227.60  
  Purchase #7 $76.60   4.857%   $80.3205   $80.32   $80.30   $80.30  
  7 purchase totals = $562.02       $605.3528   $605.34   $605.30   $605.40