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 $80.77   3.592%   $83.6713   $83.67   $83.65   $83.70  
  Purchase #2 $206.77   12.226%   $232.0497   $232.05   $232.05   $232.00  
  Purchase #3 $227.90   10.624%   $252.1121   $252.11   $252.10   $252.10  
  Purchase #4 $111.98   13.676%   $127.2944   $127.29   $127.30   $127.30  
  Purchase #5 $153.30   7.820%   $165.2881   $165.29   $165.30   $165.30  
  Purchase #6 $73.66   3.408%   $76.1703   $76.17   $76.15   $76.20  
  Purchase #7 $86.77   10.163%   $95.5884   $95.59   $95.60   $95.60  
  7 purchase totals = $941.15       $1,032.1743   $1,032.17   $1,032.15   $1,032.20