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 $156.57   13.661%   $177.959   $177.96   $177.95   $178.00  
  Purchase #2 $24.83   9.737%   $27.2477   $27.25   $27.25   $27.20  
  Purchase #3 $209.70   6.709%   $223.7688   $223.77   $223.75   $223.80  
  Purchase #4 $207.64   5.304%   $218.6532   $218.65   $218.65   $218.70  
  Purchase #5 $54.93   9.845%   $60.3379   $60.34   $60.35   $60.30  
  Purchase #6 $229.42   11.176%   $255.06   $255.06   $255.05   $255.10  
  Purchase #7 $183.57   12.465%   $206.452   $206.45   $206.45   $206.50  
  7 purchase totals = $1,066.66       $1,169.4786   $1,169.48   $1,169.45   $1,169.60