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 $24.37   11.417%   $27.1523   $27.15   $27.15   $27.20  
  Purchase #2 $132.67   12.463%   $149.2047   $149.20   $149.20   $149.20  
  Purchase #3 $218.87   13.714%   $248.8858   $248.89   $248.90   $248.90  
  Purchase #4 $200.70   3.288%   $207.299   $207.30   $207.30   $207.30  
  Purchase #5 $62.34   8.837%   $67.849   $67.85   $67.85   $67.80  
  Purchase #6 $161.28   3.171%   $166.3942   $166.39   $166.40   $166.40  
  Purchase #7 $224.56   3.654%   $232.7654   $232.77   $232.75   $232.80  
  7 purchase totals = $1,024.79       $1,099.5504   $1,099.55   $1,099.55   $1,099.60