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 $70.46   7.379%   $75.6592   $75.66   $75.65   $75.70  
  Purchase #2 $163.41   5.612%   $172.5806   $172.58   $172.60   $172.60  
  Purchase #3 $27.91   11.137%   $31.0183   $31.02   $31.00   $31.00  
  Purchase #4 $246.33   5.519%   $259.925   $259.93   $259.95   $259.90  
  Purchase #5 $46.28   5.220%   $48.6958   $48.70   $48.70   $48.70  
  Purchase #6 $197.91   12.178%   $222.0115   $222.01   $222.00   $222.00  
  Purchase #7 $136.91   7.207%   $146.7771   $146.78   $146.80   $146.80  
  7 purchase totals = $889.21       $956.6675   $956.68   $956.70   $956.70