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 $236.29   9.868%   $259.6071   $259.61   $259.60   $259.60  
  Purchase #2 $95.67   11.585%   $106.7534   $106.75   $106.75   $106.80  
  Purchase #3 $107.29   12.391%   $120.5843   $120.58   $120.60   $120.60  
  Purchase #4 $132.70   8.512%   $143.9954   $144.00   $144.00   $144.00  
  Purchase #5 $223.97   12.326%   $251.5765   $251.58   $251.60   $251.60  
  Purchase #6 $5.78   10.216%   $6.3705   $6.37   $6.35   $6.40  
  Purchase #7 $21.97   9.390%   $24.033   $24.03   $24.05   $24.00  
  7 purchase totals = $823.67       $912.9202   $912.92   $912.95   $913.00