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 $23.72   13.252%   $26.8634   $26.86   $26.85   $26.90  
  Purchase #2 $23.91   3.382%   $24.7186   $24.72   $24.70   $24.70  
  Purchase #3 $205.39   8.218%   $222.269   $222.27   $222.25   $222.30  
  Purchase #4 $237.89   12.846%   $268.4493   $268.45   $268.45   $268.40  
  Purchase #5 $202.59   11.567%   $226.0236   $226.02   $226.00   $226.00  
  Purchase #6 $30.66   13.675%   $34.8528   $34.85   $34.85   $34.90  
  Purchase #7 $233.53   11.317%   $259.9586   $259.96   $259.95   $260.00  
  7 purchase totals = $957.69       $1,063.1353   $1,063.13   $1,063.05   $1,063.20