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 $232.97   13.772%   $265.0546   $265.05   $265.05   $265.10  
  Purchase #2 $186.71   8.585%   $202.7391   $202.74   $202.75   $202.70  
  Purchase #3 $102.59   6.810%   $109.5764   $109.58   $109.60   $109.60  
  Purchase #4 $231.37   7.188%   $248.0009   $248.00   $248.00   $248.00  
  Purchase #5 $31.38   5.462%   $33.094   $33.09   $33.10   $33.10  
  Purchase #6 $102.33   8.564%   $111.0935   $111.09   $111.10   $111.10  
  Purchase #7 $12.42   3.255%   $12.8243   $12.82   $12.80   $12.80  
  7 purchase totals = $899.77       $982.3828   $982.37   $982.40   $982.40