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 $161.95   10.566%   $179.0616   $179.06   $179.05   $179.10  
  Purchase #2 $218.41   9.311%   $238.7462   $238.75   $238.75   $238.70  
  Purchase #3 $184.90   7.339%   $198.4698   $198.47   $198.45   $198.50  
  Purchase #4 $157.60   11.689%   $176.0219   $176.02   $176.00   $176.00  
  Purchase #5 $34.27   12.272%   $38.4756   $38.48   $38.50   $38.50  
  Purchase #6 $178.46   13.753%   $203.0036   $203.00   $203.00   $203.00  
  Purchase #7 $203.81   12.175%   $228.6239   $228.62   $228.60   $228.60  
  7 purchase totals = $1,139.40       $1,262.4026   $1,262.40   $1,262.35   $1,262.40