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 $81.88   13.167%   $92.6611   $92.66   $92.65   $92.70  
  Purchase #2 $72.94   13.573%   $82.8401   $82.84   $82.85   $82.80  
  Purchase #3 $24.53   11.216%   $27.2813   $27.28   $27.30   $27.30  
  Purchase #4 $214.42   7.337%   $230.152   $230.15   $230.15   $230.20  
  Purchase #5 $87.51   8.832%   $95.2389   $95.24   $95.25   $95.20  
  Purchase #6 $191.41   5.551%   $202.0352   $202.04   $202.05   $202.00  
  Purchase #7 $106.68   5.515%   $112.5634   $112.56   $112.55   $112.60  
  7 purchase totals = $779.37       $842.7720   $842.77   $842.80   $842.80