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 $54.30   8.554%   $58.9448   $58.94   $58.95   $58.90  
  Purchase #2 $203.40   8.493%   $220.6748   $220.67   $220.65   $220.70  
  Purchase #3 $11.66   9.578%   $12.7768   $12.78   $12.80   $12.80  
  Purchase #4 $218.42   12.557%   $245.847   $245.85   $245.85   $245.80  
  Purchase #5 $230.67   9.465%   $252.5029   $252.50   $252.50   $252.50  
  Purchase #6 $242.57   5.528%   $255.9793   $255.98   $256.00   $256.00  
  Purchase #7 $93.91   7.848%   $101.2801   $101.28   $101.30   $101.30  
  7 purchase totals = $1,054.93       $1,148.0057   $1,148.00   $1,148.05   $1,148.00