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 $230.61   12.734%   $259.9759   $259.98   $260.00   $260.00  
  Purchase #2 $101.26   5.327%   $106.6541   $106.65   $106.65   $106.70  
  Purchase #3 $226.93   4.326%   $236.747   $236.75   $236.75   $236.70  
  Purchase #4 $84.55   5.854%   $89.4996   $89.50   $89.50   $89.50  
  Purchase #5 $10.75   10.810%   $11.9121   $11.91   $11.90   $11.90  
  Purchase #6 $39.32   11.811%   $43.9641   $43.96   $43.95   $44.00  
  Purchase #7 $117.32   4.248%   $122.3038   $122.30   $122.30   $122.30  
  7 purchase totals = $810.74       $871.0566   $871.05   $871.05   $871.10