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 $95.92   8.420%   $103.9965   $104.00   $104.00   $104.00  
  Purchase #2 $192.93   7.788%   $207.9554   $207.96   $207.95   $208.00  
  Purchase #3 $193.46   7.307%   $207.5961   $207.60   $207.60   $207.60  
  Purchase #4 $25.79   4.120%   $26.8525   $26.85   $26.85   $26.90  
  Purchase #5 $108.67   13.191%   $123.0047   $123.00   $123.00   $123.00  
  Purchase #6 $39.58   3.779%   $41.0757   $41.08   $41.10   $41.10  
  Purchase #7 $16.70   3.334%   $17.2568   $17.26   $17.25   $17.30  
  7 purchase totals = $673.05       $727.7377   $727.75   $727.75   $727.90