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 $239.58   10.197%   $264.01   $264.01   $264.00   $264.00  
  Purchase #2 $145.31   12.116%   $162.9158   $162.92   $162.90   $162.90  
  Purchase #3 $30.30   13.339%   $34.3417   $34.34   $34.35   $34.30  
  Purchase #4 $83.27   5.502%   $87.8515   $87.85   $87.85   $87.90  
  Purchase #5 $220.45   8.522%   $239.2367   $239.24   $239.25   $239.20  
  Purchase #6 $111.88   5.588%   $118.1319   $118.13   $118.15   $118.10  
  Purchase #7 $217.79   10.851%   $241.4224   $241.42   $241.40   $241.40  
  7 purchase totals = $1,048.58       $1,147.9100   $1,147.91   $1,147.90   $1,147.80