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 $77.29   7.120%   $82.793   $82.79   $82.80   $82.80  
  Purchase #2 $250.30   7.827%   $269.891   $269.89   $269.90   $269.90  
  Purchase #3 $192.49   6.129%   $204.2877   $204.29   $204.30   $204.30  
  Purchase #4 $53.42   13.757%   $60.769   $60.77   $60.75   $60.80  
  Purchase #5 $239.85   8.364%   $259.9111   $259.91   $259.90   $259.90  
  Purchase #6 $86.69   13.652%   $98.5249   $98.52   $98.50   $98.50  
  Purchase #7 $245.30   12.843%   $276.8039   $276.80   $276.80   $276.80  
  7 purchase totals = $1,145.34       $1,252.9806   $1,252.97   $1,252.95   $1,253.00