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 $207.71   13.166%   $235.0571   $235.06   $235.05   $235.10  
  Purchase #2 $151.75   10.274%   $167.3408   $167.34   $167.35   $167.30  
  Purchase #3 $6.68   4.679%   $6.9926   $6.99   $7.00   $7.00  
  Purchase #4 $40.71   10.854%   $45.1287   $45.13   $45.15   $45.10  
  Purchase #5 $202.69   3.386%   $209.5531   $209.55   $209.55   $209.60  
  Purchase #6 $158.99   9.746%   $174.4852   $174.49   $174.50   $174.50  
  Purchase #7 $79.86   7.589%   $85.9206   $85.92   $85.90   $85.90  
  7 purchase totals = $848.39       $924.4781   $924.48   $924.50   $924.50