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 $29.61   5.603%   $31.269   $31.27   $31.25   $31.30  
  Purchase #2 $113.81   4.645%   $119.0965   $119.10   $119.10   $119.10  
  Purchase #3 $200.93   3.727%   $208.4187   $208.42   $208.40   $208.40  
  Purchase #4 $158.57   13.173%   $179.4584   $179.46   $179.45   $179.50  
  Purchase #5 $194.69   6.624%   $207.5863   $207.59   $207.60   $207.60  
  Purchase #6 $81.98   6.461%   $87.2767   $87.28   $87.30   $87.30  
  Purchase #7 $56.35   7.421%   $60.5317   $60.53   $60.55   $60.50  
  7 purchase totals = $835.94       $893.6373   $893.65   $893.65   $893.70