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 $166.97   11.163%   $185.6089   $185.61   $185.60   $185.60  
  Purchase #2 $13.39   7.632%   $14.4119   $14.41   $14.40   $14.40  
  Purchase #3 $55.28   12.107%   $61.9727   $61.97   $61.95   $62.00  
  Purchase #4 $60.80   11.181%   $67.598   $67.60   $67.60   $67.60  
  Purchase #5 $242.28   6.658%   $258.411   $258.41   $258.40   $258.40  
  Purchase #6 $176.41   6.398%   $187.6967   $187.70   $187.70   $187.70  
  Purchase #7 $31.75   5.167%   $33.3905   $33.39   $33.40   $33.40  
  7 purchase totals = $746.88       $809.0897   $809.09   $809.05   $809.10