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 $211.77   13.813%   $241.0218   $241.02   $241.00   $241.00  
  Purchase #2 $177.73   6.541%   $189.3553   $189.36   $189.35   $189.40  
  Purchase #3 $10.86   13.456%   $12.3213   $12.32   $12.30   $12.30  
  Purchase #4 $166.87   8.695%   $181.3793   $181.38   $181.40   $181.40  
  Purchase #5 $130.34   4.621%   $136.363   $136.36   $136.35   $136.40  
  Purchase #6 $98.99   6.676%   $105.5986   $105.60   $105.60   $105.60  
  Purchase #7 $174.39   10.387%   $192.5039   $192.50   $192.50   $192.50  
  7 purchase totals = $970.95       $1,058.5432   $1,058.54   $1,058.50   $1,058.60