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 $181.65   13.488%   $206.151   $206.15   $206.15   $206.20  
  Purchase #2 $155.26   12.568%   $174.7731   $174.77   $174.75   $174.80  
  Purchase #3 $47.46   9.566%   $52   $52.00   $52.00   $52.00  
  Purchase #4 $68.75   5.654%   $72.6371   $72.64   $72.65   $72.60  
  Purchase #5 $186.45   4.341%   $194.5438   $194.54   $194.55   $194.50  
  Purchase #6 $65.74   8.713%   $71.4679   $71.47   $71.45   $71.50  
  Purchase #7 $22.51   11.271%   $25.0471   $25.05   $25.05   $25.00  
  7 purchase totals = $727.82       $796.6200   $796.62   $796.60   $796.60