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 $137.82   11.723%   $153.9766   $153.98   $154.00   $154.00  
  Purchase #2 $48.59   9.844%   $53.3732   $53.37   $53.35   $53.40  
  Purchase #3 $159.82   13.610%   $181.5715   $181.57   $181.55   $181.60  
  Purchase #4 $187.72   10.733%   $207.868   $207.87   $207.85   $207.90  
  Purchase #5 $221.67   6.221%   $235.4601   $235.46   $235.45   $235.50  
  Purchase #6 $196.72   7.713%   $211.893   $211.89   $211.90   $211.90  
  Purchase #7 $20.29   13.553%   $23.0399   $23.04   $23.05   $23.00  
  7 purchase totals = $972.63       $1,067.1823   $1,067.18   $1,067.15   $1,067.30