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 $87.55   10.462%   $96.7095   $96.71   $96.70   $96.70  
  Purchase #2 $187.53   6.765%   $200.2164   $200.22   $200.20   $200.20  
  Purchase #3 $56.39   3.240%   $58.217   $58.22   $58.20   $58.20  
  Purchase #4 $31.54   6.396%   $33.5573   $33.56   $33.55   $33.60  
  Purchase #5 $163.39   7.201%   $175.1557   $175.16   $175.15   $175.20  
  Purchase #6 $61.82   11.840%   $69.1395   $69.14   $69.15   $69.10  
  Purchase #7 $87.43   13.563%   $99.2881   $99.29   $99.30   $99.30  
  7 purchase totals = $675.65       $732.2835   $732.30   $732.25   $732.30