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 $241.57   9.709%   $265.024   $265.02   $265.00   $265.00  
  Purchase #2 $42.99   3.515%   $44.5011   $44.50   $44.50   $44.50  
  Purchase #3 $237.89   10.256%   $262.288   $262.29   $262.30   $262.30  
  Purchase #4 $54.67   3.441%   $56.5512   $56.55   $56.55   $56.60  
  Purchase #5 $166.33   8.740%   $180.8672   $180.87   $180.85   $180.90  
  Purchase #6 $104.44   3.323%   $107.9105   $107.91   $107.90   $107.90  
  Purchase #7 $230.78   5.128%   $242.6144   $242.61   $242.60   $242.60  
  7 purchase totals = $1,078.67       $1,159.7564   $1,159.75   $1,159.70   $1,159.80