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 $167.93   8.718%   $182.5701   $182.57   $182.55   $182.60  
  Purchase #2 $55.88   7.406%   $60.0185   $60.02   $60.00   $60.00  
  Purchase #3 $90.40   6.350%   $96.1404   $96.14   $96.15   $96.10  
  Purchase #4 $237.49   12.160%   $266.3688   $266.37   $266.35   $266.40  
  Purchase #5 $74.45   7.870%   $80.3092   $80.31   $80.30   $80.30  
  Purchase #6 $151.72   8.231%   $164.2081   $164.21   $164.20   $164.20  
  Purchase #7 $172.29   8.685%   $187.2534   $187.25   $187.25   $187.30  
  7 purchase totals = $950.16       $1,036.8685   $1,036.87   $1,036.80   $1,036.90