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 $243.75   10.618%   $269.6314   $269.63   $269.65   $269.60  
  Purchase #2 $167.92   10.512%   $185.5718   $185.57   $185.55   $185.60  
  Purchase #3 $222.64   5.696%   $235.3216   $235.32   $235.30   $235.30  
  Purchase #4 $92.75   5.863%   $98.1879   $98.19   $98.20   $98.20  
  Purchase #5 $174.60   3.592%   $180.8716   $180.87   $180.85   $180.90  
  Purchase #6 $51.49   8.250%   $55.7379   $55.74   $55.75   $55.70  
  Purchase #7 $201.56   12.767%   $227.2932   $227.29   $227.30   $227.30  
  7 purchase totals = $1,154.71       $1,252.6154   $1,252.61   $1,252.60   $1,252.60