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 $207.79   12.210%   $233.1612   $233.16   $233.15   $233.20  
  Purchase #2 $79.59   6.346%   $84.6408   $84.64   $84.65   $84.60  
  Purchase #3 $81.66   6.546%   $87.0055   $87.01   $87.00   $87.00  
  Purchase #4 $250.45   11.341%   $278.8535   $278.85   $278.85   $278.90  
  Purchase #5 $104.39   6.856%   $111.547   $111.55   $111.55   $111.50  
  Purchase #6 $151.25   9.645%   $165.8381   $165.84   $165.85   $165.80  
  Purchase #7 $177.88   13.866%   $202.5448   $202.54   $202.55   $202.50  
  7 purchase totals = $1,053.01       $1,163.5909   $1,163.59   $1,163.60   $1,163.50