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 $29.82   11.312%   $33.1932   $33.19   $33.20   $33.20  
  Purchase #2 $226.46   10.393%   $249.996   $250.00   $250.00   $250.00  
  Purchase #3 $187.63   4.458%   $195.9945   $195.99   $196.00   $196.00  
  Purchase #4 $23.72   13.471%   $26.9153   $26.92   $26.90   $26.90  
  Purchase #5 $153.64   9.140%   $167.6827   $167.68   $167.70   $167.70  
  Purchase #6 $130.31   11.640%   $145.4781   $145.48   $145.50   $145.50  
  Purchase #7 $46.37   11.536%   $51.7192   $51.72   $51.70   $51.70  
  7 purchase totals = $797.95       $870.9790   $870.98   $871.00   $871.00