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 $207.52   13.127%   $234.7612   $234.76   $234.75   $234.80  
  Purchase #2 $160.45   11.259%   $178.5151   $178.52   $178.50   $178.50  
  Purchase #3 $249.80   13.354%   $283.1583   $283.16   $283.15   $283.20  
  Purchase #4 $229.56   5.806%   $242.8883   $242.89   $242.90   $242.90  
  Purchase #5 $108.50   8.235%   $117.435   $117.44   $117.45   $117.40  
  Purchase #6 $41.92   9.687%   $45.9808   $45.98   $46.00   $46.00  
  Purchase #7 $235.32   11.457%   $262.2806   $262.28   $262.30   $262.30  
  7 purchase totals = $1,233.07       $1,365.0193   $1,365.03   $1,365.05   $1,365.10