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 $196.32   13.731%   $223.2767   $223.28   $223.30   $223.30  
  Purchase #2 $23.62   13.256%   $26.7511   $26.75   $26.75   $26.80  
  Purchase #3 $177.62   8.549%   $192.8047   $192.80   $192.80   $192.80  
  Purchase #4 $95.90   8.467%   $104.0199   $104.02   $104.00   $104.00  
  Purchase #5 $200.99   3.626%   $208.2779   $208.28   $208.30   $208.30  
  Purchase #6 $165.43   5.518%   $174.5584   $174.56   $174.55   $174.60  
  Purchase #7 $104.98   10.300%   $115.7929   $115.79   $115.80   $115.80  
  7 purchase totals = $964.86       $1,045.4816   $1,045.48   $1,045.50   $1,045.60