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 $167.53   11.568%   $186.9099   $186.91   $186.90   $186.90  
  Purchase #2 $14.36   11.769%   $16.05   $16.05   $16.05   $16.10  
  Purchase #3 $113.35   3.769%   $117.6222   $117.62   $117.60   $117.60  
  Purchase #4 $240.88   4.271%   $251.168   $251.17   $251.15   $251.20  
  Purchase #5 $232.70   7.652%   $250.5062   $250.51   $250.50   $250.50  
  Purchase #6 $116.26   11.318%   $129.4183   $129.42   $129.40   $129.40  
  Purchase #7 $148.93   11.189%   $165.5938   $165.59   $165.60   $165.60  
  7 purchase totals = $1,034.01       $1,117.2684   $1,117.27   $1,117.20   $1,117.30