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 $231.83   7.306%   $248.7675   $248.77   $248.75   $248.80  
  Purchase #2 $113.41   11.692%   $126.6699   $126.67   $126.65   $126.70  
  Purchase #3 $160.92   11.357%   $179.1957   $179.20   $179.20   $179.20  
  Purchase #4 $238.73   8.685%   $259.4637   $259.46   $259.45   $259.50  
  Purchase #5 $243.77   11.475%   $271.7426   $271.74   $271.75   $271.70  
  Purchase #6 $62.90   11.469%   $70.114   $70.11   $70.10   $70.10  
  Purchase #7 $220.88   6.165%   $234.4973   $234.50   $234.50   $234.50  
  7 purchase totals = $1,272.44       $1,390.4507   $1,390.45   $1,390.40   $1,390.50