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 $195.59   12.289%   $219.6261   $219.63   $219.65   $219.60  
  Purchase #2 $8.26   8.716%   $8.9799   $8.98   $9.00   $9.00  
  Purchase #3 $214.48   13.177%   $242.742   $242.74   $242.75   $242.70  
  Purchase #4 $239.64   6.851%   $256.0577   $256.06   $256.05   $256.10  
  Purchase #5 $81.82   7.375%   $87.8542   $87.85   $87.85   $87.90  
  Purchase #6 $151.31   13.304%   $171.4403   $171.44   $171.45   $171.40  
  Purchase #7 $65.59   5.593%   $69.2584   $69.26   $69.25   $69.30  
  7 purchase totals = $956.69       $1,055.9586   $1,055.96   $1,056.00   $1,056.00