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 $71.95   7.687%   $77.4808   $77.48   $77.50   $77.50  
  Purchase #2 $110.73   4.443%   $115.6497   $115.65   $115.65   $115.60  
  Purchase #3 $160.64   4.335%   $167.6037   $167.60   $167.60   $167.60  
  Purchase #4 $249.25   11.838%   $278.7562   $278.76   $278.75   $278.80  
  Purchase #5 $169.63   4.506%   $177.2735   $177.27   $177.25   $177.30  
  Purchase #6 $77.48   7.296%   $83.1329   $83.13   $83.15   $83.10  
  Purchase #7 $209.89   8.643%   $228.0308   $228.03   $228.05   $228.00  
  7 purchase totals = $1,049.57       $1,127.9276   $1,127.92   $1,127.95   $1,127.90