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 $132.74   8.472%   $143.9857   $143.99   $144.00   $144.00  
  Purchase #2 $86.75   10.349%   $95.7278   $95.73   $95.75   $95.70  
  Purchase #3 $177.44   13.558%   $201.4973   $201.50   $201.50   $201.50  
  Purchase #4 $145.74   3.117%   $150.2827   $150.28   $150.30   $150.30  
  Purchase #5 $113.81   3.378%   $117.6545   $117.65   $117.65   $117.70  
  Purchase #6 $124.68   4.269%   $130.0026   $130.00   $130.00   $130.00  
  Purchase #7 $104.79   8.841%   $114.0545   $114.05   $114.05   $114.10  
  7 purchase totals = $885.95       $953.2051   $953.20   $953.25   $953.30