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 $52.65   7.621%   $56.6625   $56.66   $56.65   $56.70  
  Purchase #2 $189.99   5.455%   $200.354   $200.35   $200.35   $200.40  
  Purchase #3 $198.74   12.327%   $223.2387   $223.24   $223.25   $223.20  
  Purchase #4 $214.91   13.603%   $244.1442   $244.14   $244.15   $244.10  
  Purchase #5 $50.97   11.834%   $57.0018   $57.00   $57.00   $57.00  
  Purchase #6 $222.36   6.360%   $236.5021   $236.50   $236.50   $236.50  
  Purchase #7 $169.64   4.157%   $176.6919   $176.69   $176.70   $176.70  
  7 purchase totals = $1,099.26       $1,194.5952   $1,194.58   $1,194.60   $1,194.60