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 $33.26   3.692%   $34.488   $34.49   $34.50   $34.50  
  Purchase #2 $101.49   6.334%   $107.9184   $107.92   $107.90   $107.90  
  Purchase #3 $108.37   6.559%   $115.478   $115.48   $115.50   $115.50  
  Purchase #4 $88.58   7.644%   $95.3511   $95.35   $95.35   $95.40  
  Purchase #5 $196.30   10.632%   $217.1706   $217.17   $217.15   $217.20  
  Purchase #6 $28.35   7.249%   $30.4051   $30.41   $30.40   $30.40  
  Purchase #7 $220.62   6.283%   $234.4816   $234.48   $234.50   $234.50  
  7 purchase totals = $776.97       $835.2928   $835.30   $835.30   $835.40