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 $238.98   8.246%   $258.6863   $258.69   $258.70   $258.70  
  Purchase #2 $168.26   9.800%   $184.7495   $184.75   $184.75   $184.70  
  Purchase #3 $243.41   9.441%   $266.3903   $266.39   $266.40   $266.40  
  Purchase #4 $26.26   9.676%   $28.8009   $28.80   $28.80   $28.80  
  Purchase #5 $48.95   5.423%   $51.6046   $51.60   $51.60   $51.60  
  Purchase #6 $132.58   5.150%   $139.4079   $139.41   $139.40   $139.40  
  Purchase #7 $213.92   11.723%   $238.9978   $239.00   $239.00   $239.00  
  7 purchase totals = $1,072.36       $1,168.6373   $1,168.64   $1,168.65   $1,168.60