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 $29.50   5.508%   $31.1249   $31.12   $31.10   $31.10  
  Purchase #2 $5.71   6.665%   $6.0906   $6.09   $6.10   $6.10  
  Purchase #3 $92.41   6.109%   $98.0553   $98.06   $98.05   $98.10  
  Purchase #4 $32.50   12.227%   $36.4738   $36.47   $36.45   $36.50  
  Purchase #5 $151.39   3.780%   $157.1125   $157.11   $157.10   $157.10  
  Purchase #6 $190.57   11.275%   $212.0568   $212.06   $212.05   $212.10  
  Purchase #7 $31.76   7.488%   $34.1382   $34.14   $34.15   $34.10  
  7 purchase totals = $533.84       $575.0521   $575.05   $575.00   $575.10