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 $152.38   13.551%   $173.029   $173.03   $173.05   $173.00  
  Purchase #2 $246.41   7.819%   $265.6768   $265.68   $265.70   $265.70  
  Purchase #3 $82.52   12.368%   $92.7261   $92.73   $92.75   $92.70  
  Purchase #4 $179.93   9.798%   $197.5595   $197.56   $197.55   $197.60  
  Purchase #5 $95.44   3.574%   $98.851   $98.85   $98.85   $98.90  
  Purchase #6 $33.52   11.792%   $37.4727   $37.47   $37.45   $37.50  
  Purchase #7 $149.73   9.298%   $163.6519   $163.65   $163.65   $163.70  
  7 purchase totals = $939.93       $1,028.9670   $1,028.97   $1,029.00   $1,029.10