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 $46.74   12.506%   $52.5853   $52.59   $52.60   $52.60  
  Purchase #2 $242.65   10.532%   $268.2059   $268.21   $268.20   $268.20  
  Purchase #3 $153.89   5.441%   $162.2632   $162.26   $162.25   $162.30  
  Purchase #4 $123.43   12.149%   $138.4255   $138.43   $138.45   $138.40  
  Purchase #5 $82.41   9.645%   $90.3584   $90.36   $90.35   $90.40  
  Purchase #6 $93.92   12.226%   $105.4027   $105.40   $105.40   $105.40  
  Purchase #7 $236.65   8.603%   $257.009   $257.01   $257.00   $257.00  
  7 purchase totals = $979.69       $1,074.2500   $1,074.26   $1,074.25   $1,074.30