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 $83.89   11.654%   $93.6665   $93.67   $93.65   $93.70  
  Purchase #2 $220.73   12.108%   $247.456   $247.46   $247.45   $247.50  
  Purchase #3 $38.57   4.114%   $40.1568   $40.16   $40.15   $40.20  
  Purchase #4 $227.70   13.824%   $259.1772   $259.18   $259.20   $259.20  
  Purchase #5 $21.69   11.452%   $24.1739   $24.17   $24.15   $24.20  
  Purchase #6 $65.61   11.248%   $72.9898   $72.99   $73.00   $73.00  
  Purchase #7 $201.41   6.340%   $214.1794   $214.18   $214.20   $214.20  
  7 purchase totals = $859.60       $951.7996   $951.81   $951.80   $952.00