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 $48.38   12.761%   $54.5538   $54.55   $54.55   $54.60  
  Purchase #2 $239.92   4.714%   $251.2298   $251.23   $251.25   $251.20  
  Purchase #3 $179.31   11.469%   $199.8751   $199.88   $199.90   $199.90  
  Purchase #4 $221.36   4.424%   $231.153   $231.15   $231.15   $231.20  
  Purchase #5 $27.98   8.634%   $30.3958   $30.40   $30.40   $30.40  
  Purchase #6 $248.71   9.419%   $272.136   $272.14   $272.15   $272.10  
  Purchase #7 $24.28   5.632%   $25.6474   $25.65   $25.65   $25.60  
  7 purchase totals = $989.94       $1,064.9909   $1,065.00   $1,065.05   $1,065.00