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 $154.36   9.656%   $169.265   $169.27   $169.25   $169.30  
  Purchase #2 $127.53   6.858%   $136.276   $136.28   $136.30   $136.30  
  Purchase #3 $211.78   9.566%   $232.0389   $232.04   $232.05   $232.00  
  Purchase #4 $95.83   9.703%   $105.1284   $105.13   $105.15   $105.10  
  Purchase #5 $242.44   11.313%   $269.8672   $269.87   $269.85   $269.90  
  Purchase #6 $60.74   12.314%   $68.2195   $68.22   $68.20   $68.20  
  Purchase #7 $74.94   12.868%   $84.5833   $84.58   $84.60   $84.60  
  7 purchase totals = $967.62       $1,065.3783   $1,065.39   $1,065.40   $1,065.40