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 $92.69   3.794%   $96.2067   $96.21   $96.20   $96.20  
  Purchase #2 $150.97   9.287%   $164.9906   $164.99   $165.00   $165.00  
  Purchase #3 $6.31   9.556%   $6.913   $6.91   $6.90   $6.90  
  Purchase #4 $152.98   13.684%   $173.9138   $173.91   $173.90   $173.90  
  Purchase #5 $210.56   8.652%   $228.7777   $228.78   $228.80   $228.80  
  Purchase #6 $163.57   13.190%   $185.1449   $185.14   $185.15   $185.10  
  Purchase #7 $77.91   10.668%   $86.2214   $86.22   $86.20   $86.20  
  7 purchase totals = $854.99       $942.1681   $942.16   $942.15   $942.10