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 $235.99   11.377%   $262.8386   $262.84   $262.85   $262.80  
  Purchase #2 $107.35   13.386%   $121.7199   $121.72   $121.70   $121.70  
  Purchase #3 $8.93   10.609%   $9.8774   $9.88   $9.90   $9.90  
  Purchase #4 $112.55   10.735%   $124.6322   $124.63   $124.65   $124.60  
  Purchase #5 $60.75   7.277%   $65.1708   $65.17   $65.15   $65.20  
  Purchase #6 $246.40   8.189%   $266.5777   $266.58   $266.60   $266.60  
  Purchase #7 $13.41   10.238%   $14.7829   $14.78   $14.80   $14.80  
  7 purchase totals = $785.38       $865.5995   $865.60   $865.65   $865.60