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 $61.68   12.541%   $69.4153   $69.42   $69.40   $69.40  
  Purchase #2 $30.41   7.535%   $32.7014   $32.70   $32.70   $32.70  
  Purchase #3 $76.75   5.843%   $81.2345   $81.23   $81.25   $81.20  
  Purchase #4 $135.65   12.385%   $152.4503   $152.45   $152.45   $152.50  
  Purchase #5 $144.33   11.638%   $161.1271   $161.13   $161.15   $161.10  
  Purchase #6 $95.74   6.791%   $102.2417   $102.24   $102.25   $102.20  
  Purchase #7 $129.83   13.541%   $147.4103   $147.41   $147.40   $147.40  
  7 purchase totals = $674.39       $746.5806   $746.58   $746.60   $746.50