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 $200.28   13.327%   $226.9713   $226.97   $226.95   $227.00  
  Purchase #2 $29.36   3.370%   $30.3494   $30.35   $30.35   $30.30  
  Purchase #3 $59.41   8.346%   $64.3684   $64.37   $64.35   $64.40  
  Purchase #4 $165.47   3.640%   $171.4931   $171.49   $171.50   $171.50  
  Purchase #5 $160.59   8.307%   $173.9302   $173.93   $173.95   $173.90  
  Purchase #6 $119.27   10.455%   $131.7397   $131.74   $131.75   $131.70  
  Purchase #7 $166.57   5.331%   $175.4498   $175.45   $175.45   $175.40  
  7 purchase totals = $900.95       $974.3019   $974.30   $974.30   $974.20