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 $187.67   4.573%   $196.2521   $196.25   $196.25   $196.30  
  Purchase #2 $58.85   3.486%   $60.9015   $60.90   $60.90   $60.90  
  Purchase #3 $192.87   13.128%   $218.19   $218.19   $218.20   $218.20  
  Purchase #4 $132.85   10.156%   $146.3422   $146.34   $146.35   $146.30  
  Purchase #5 $232.94   9.672%   $255.47   $255.47   $255.45   $255.50  
  Purchase #6 $163.65   13.777%   $186.1961   $186.20   $186.20   $186.20  
  Purchase #7 $60.83   12.309%   $68.3176   $68.32   $68.30   $68.30  
  7 purchase totals = $1,029.66       $1,131.6695   $1,131.67   $1,131.65   $1,131.70