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 $149.77   12.135%   $167.9446   $167.94   $167.95   $167.90  
  Purchase #2 $31.62   3.424%   $32.7027   $32.70   $32.70   $32.70  
  Purchase #3 $119.34   9.408%   $130.5675   $130.57   $130.55   $130.60  
  Purchase #4 $232.54   3.326%   $240.2743   $240.27   $240.25   $240.30  
  Purchase #5 $146.92   12.262%   $164.9353   $164.94   $164.95   $164.90  
  Purchase #6 $206.48   6.609%   $220.1263   $220.13   $220.15   $220.10  
  Purchase #7 $189.64   3.433%   $196.1503   $196.15   $196.15   $196.20  
  7 purchase totals = $1,076.31       $1,152.7010   $1,152.70   $1,152.70   $1,152.70