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 $246.47   10.258%   $271.7529   $271.75   $271.75   $271.80  
  Purchase #2 $215.62   4.205%   $224.6868   $224.69   $224.70   $224.70  
  Purchase #3 $127.63   5.378%   $134.4939   $134.49   $134.50   $134.50  
  Purchase #4 $27.56   12.308%   $30.9521   $30.95   $30.95   $31.00  
  Purchase #5 $172.88   10.291%   $190.6711   $190.67   $190.65   $190.70  
  Purchase #6 $203.75   13.109%   $230.4596   $230.46   $230.45   $230.50  
  Purchase #7 $40.43   8.385%   $43.8201   $43.82   $43.80   $43.80  
  7 purchase totals = $1,034.34       $1,126.8365   $1,126.83   $1,126.80   $1,127.00