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 $184.45   12.374%   $207.2738   $207.27   $207.25   $207.30  
  Purchase #2 $152.99   9.569%   $167.6296   $167.63   $167.65   $167.60  
  Purchase #3 $222.69   12.564%   $250.6688   $250.67   $250.65   $250.70  
  Purchase #4 $170.77   7.236%   $183.1269   $183.13   $183.15   $183.10  
  Purchase #5 $167.28   10.454%   $184.7675   $184.77   $184.75   $184.80  
  Purchase #6 $243.61   13.300%   $276.0101   $276.01   $276.00   $276.00  
  Purchase #7 $84.94   12.522%   $95.5762   $95.58   $95.60   $95.60  
  7 purchase totals = $1,226.73       $1,365.0529   $1,365.06   $1,365.05   $1,365.10