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 $246.50   9.199%   $269.1755   $269.18   $269.20   $269.20  
  Purchase #2 $227.30   11.682%   $253.8532   $253.85   $253.85   $253.90  
  Purchase #3 $224.89   4.841%   $235.7769   $235.78   $235.80   $235.80  
  Purchase #4 $60.91   6.212%   $64.6937   $64.69   $64.70   $64.70  
  Purchase #5 $248.32   6.248%   $263.835   $263.84   $263.85   $263.80  
  Purchase #6 $38.88   5.667%   $41.0833   $41.08   $41.10   $41.10  
  Purchase #7 $242.63   8.639%   $263.5908   $263.59   $263.60   $263.60  
  7 purchase totals = $1,289.43       $1,392.0084   $1,392.01   $1,392.10   $1,392.10