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 $62.47   11.221%   $69.4798   $69.48   $69.50   $69.50  
  Purchase #2 $102.63   9.691%   $112.5759   $112.58   $112.60   $112.60  
  Purchase #3 $202.83   13.384%   $229.9768   $229.98   $230.00   $230.00  
  Purchase #4 $44.36   12.512%   $49.9103   $49.91   $49.90   $49.90  
  Purchase #5 $65.40   3.794%   $67.8813   $67.88   $67.90   $67.90  
  Purchase #6 $17.90   8.805%   $19.4761   $19.48   $19.50   $19.50  
  Purchase #7 $181.98   13.654%   $206.8275   $206.83   $206.85   $206.80  
  7 purchase totals = $677.57       $756.1277   $756.14   $756.25   $756.20