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 $167.65   6.856%   $179.1441   $179.14   $179.15   $179.10  
  Purchase #2 $229.48   7.342%   $246.3284   $246.33   $246.35   $246.30  
  Purchase #3 $200.92   3.172%   $207.2932   $207.29   $207.30   $207.30  
  Purchase #4 $152.62   10.271%   $168.2956   $168.30   $168.30   $168.30  
  Purchase #5 $44.82   6.562%   $47.7611   $47.76   $47.75   $47.80  
  Purchase #6 $103.76   11.791%   $115.9943   $115.99   $116.00   $116.00  
  Purchase #7 $173.37   10.421%   $191.4369   $191.44   $191.45   $191.40  
  7 purchase totals = $1,072.62       $1,156.2536   $1,156.25   $1,156.30   $1,156.20