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 $90.41   8.692%   $98.2684   $98.27   $98.25   $98.30  
  Purchase #2 $145.83   11.537%   $162.6544   $162.65   $162.65   $162.70  
  Purchase #3 $73.74   9.109%   $80.457   $80.46   $80.45   $80.50  
  Purchase #4 $42.57   3.450%   $44.0387   $44.04   $44.05   $44.00  
  Purchase #5 $34.48   6.655%   $36.7746   $36.77   $36.75   $36.80  
  Purchase #6 $190.90   4.766%   $199.9983   $200.00   $200.00   $200.00  
  Purchase #7 $126.44   8.701%   $137.4415   $137.44   $137.45   $137.40  
  7 purchase totals = $704.37       $759.6329   $759.63   $759.60   $759.70