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 $240.35   8.113%   $259.8496   $259.85   $259.85   $259.80  
  Purchase #2 $33.77   7.184%   $36.196   $36.20   $36.20   $36.20  
  Purchase #3 $37.65   12.216%   $42.2493   $42.25   $42.25   $42.20  
  Purchase #4 $200.96   7.733%   $216.5002   $216.50   $216.50   $216.50  
  Purchase #5 $162.92   8.162%   $176.2175   $176.22   $176.20   $176.20  
  Purchase #6 $151.94   9.513%   $166.3941   $166.39   $166.40   $166.40  
  Purchase #7 $161.52   11.146%   $179.523   $179.52   $179.50   $179.50  
  7 purchase totals = $989.11       $1,076.9297   $1,076.93   $1,076.90   $1,076.80