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 $185.59   8.507%   $201.3781   $201.38   $201.40   $201.40  
  Purchase #2 $13.29   5.356%   $14.0018   $14.00   $14.00   $14.00  
  Purchase #3 $165.37   7.311%   $177.4602   $177.46   $177.45   $177.50  
  Purchase #4 $60.28   10.679%   $66.7173   $66.72   $66.70   $66.70  
  Purchase #5 $68.59   7.204%   $73.5312   $73.53   $73.55   $73.50  
  Purchase #6 $183.53   4.655%   $192.0733   $192.07   $192.05   $192.10  
  Purchase #7 $245.34   12.392%   $275.7425   $275.74   $275.75   $275.70  
  7 purchase totals = $921.99       $1,000.9044   $1,000.90   $1,000.90   $1,000.90