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 $86.30   7.871%   $93.0927   $93.09   $93.10   $93.10  
  Purchase #2 $186.70   8.630%   $202.8122   $202.81   $202.80   $202.80  
  Purchase #3 $194.85   3.226%   $201.1359   $201.14   $201.15   $201.10  
  Purchase #4 $72.78   6.460%   $77.4816   $77.48   $77.50   $77.50  
  Purchase #5 $197.30   6.613%   $210.3474   $210.35   $210.35   $210.30  
  Purchase #6 $168.56   9.515%   $184.5985   $184.60   $184.60   $184.60  
  Purchase #7 $224.46   4.399%   $234.334   $234.33   $234.35   $234.30  
  7 purchase totals = $1,130.95       $1,203.8023   $1,203.80   $1,203.85   $1,203.70