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 $59.52   8.298%   $64.459   $64.46   $64.45   $64.50  
  Purchase #2 $196.54   4.458%   $205.3018   $205.30   $205.30   $205.30  
  Purchase #3 $14.28   5.671%   $15.0898   $15.09   $15.10   $15.10  
  Purchase #4 $169.78   11.155%   $188.719   $188.72   $188.70   $188.70  
  Purchase #5 $120.29   11.393%   $133.9946   $133.99   $134.00   $134.00  
  Purchase #6 $160.68   11.548%   $179.2353   $179.24   $179.25   $179.20  
  Purchase #7 $121.82   8.395%   $132.0468   $132.05   $132.05   $132.00  
  7 purchase totals = $842.91       $918.8463   $918.85   $918.85   $918.80