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 $61.60   5.402%   $64.9276   $64.93   $64.95   $64.90  
  Purchase #2 $141.66   6.564%   $150.9586   $150.96   $150.95   $151.00  
  Purchase #3 $176.75   3.422%   $182.7984   $182.80   $182.80   $182.80  
  Purchase #4 $167.56   10.371%   $184.9376   $184.94   $184.95   $184.90  
  Purchase #5 $214.45   11.479%   $239.0667   $239.07   $239.05   $239.10  
  Purchase #6 $39.74   7.254%   $42.6227   $42.62   $42.60   $42.60  
  Purchase #7 $142.32   13.184%   $161.0835   $161.08   $161.10   $161.10  
  7 purchase totals = $944.08       $1,026.3951   $1,026.40   $1,026.40   $1,026.40