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 $69.62   11.251%   $77.4529   $77.45   $77.45   $77.50  
  Purchase #2 $191.53   5.168%   $201.4283   $201.43   $201.45   $201.40  
  Purchase #3 $174.77   6.505%   $186.1388   $186.14   $186.15   $186.10  
  Purchase #4 $58.32   10.601%   $64.5025   $64.50   $64.50   $64.50  
  Purchase #5 $127.75   4.157%   $133.0606   $133.06   $133.05   $133.10  
  Purchase #6 $212.43   8.635%   $230.7733   $230.77   $230.75   $230.80  
  Purchase #7 $125.45   4.170%   $130.6813   $130.68   $130.70   $130.70  
  7 purchase totals = $959.87       $1,024.0377   $1,024.03   $1,024.05   $1,024.10