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 $62.27   8.481%   $67.5511   $67.55   $67.55   $67.60  
  Purchase #2 $167.68   7.733%   $180.6467   $180.65   $180.65   $180.60  
  Purchase #3 $114.36   8.469%   $124.0451   $124.05   $124.05   $124.00  
  Purchase #4 $26.93   10.287%   $29.7003   $29.70   $29.70   $29.70  
  Purchase #5 $48.40   12.604%   $54.5003   $54.50   $54.50   $54.50  
  Purchase #6 $173.61   3.536%   $179.7488   $179.75   $179.75   $179.70  
  Purchase #7 $210.25   10.457%   $232.2358   $232.24   $232.25   $232.20  
  7 purchase totals = $803.50       $868.4281   $868.44   $868.45   $868.30