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 $162.50   11.737%   $181.5726   $181.57   $181.55   $181.60  
  Purchase #2 $241.63   5.744%   $255.5092   $255.51   $255.50   $255.50  
  Purchase #3 $157.34   8.765%   $171.1309   $171.13   $171.15   $171.10  
  Purchase #4 $76.57   4.379%   $79.923   $79.92   $79.90   $79.90  
  Purchase #5 $207.43   4.457%   $216.6752   $216.68   $216.70   $216.70  
  Purchase #6 $6.28   12.851%   $7.087   $7.09   $7.10   $7.10  
  Purchase #7 $92.44   7.315%   $99.202   $99.20   $99.20   $99.20  
  7 purchase totals = $944.19       $1,011.0999   $1,011.10   $1,011.10   $1,011.10