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 $214.39   5.511%   $226.205   $226.21   $226.20   $226.20  
  Purchase #2 $88.70   7.755%   $95.5787   $95.58   $95.60   $95.60  
  Purchase #3 $236.70   4.218%   $246.684   $246.68   $246.70   $246.70  
  Purchase #4 $66.57   5.572%   $70.2793   $70.28   $70.30   $70.30  
  Purchase #5 $96.42   10.396%   $106.4438   $106.44   $106.45   $106.40  
  Purchase #6 $72.36   6.511%   $77.0714   $77.07   $77.05   $77.10  
  Purchase #7 $169.84   3.277%   $175.4057   $175.41   $175.40   $175.40  
  7 purchase totals = $944.98       $997.6679   $997.67   $997.70   $997.70