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 $185.65   8.784%   $201.9575   $201.96   $201.95   $202.00  
  Purchase #2 $153.32   6.818%   $163.7734   $163.77   $163.75   $163.80  
  Purchase #3 $18.72   4.165%   $19.4997   $19.50   $19.50   $19.50  
  Purchase #4 $139.28   5.468%   $146.8958   $146.90   $146.90   $146.90  
  Purchase #5 $21.50   13.220%   $24.3423   $24.34   $24.35   $24.30  
  Purchase #6 $161.40   10.585%   $178.4842   $178.48   $178.50   $178.50  
  Purchase #7 $38.49   5.171%   $40.4803   $40.48   $40.50   $40.50  
  7 purchase totals = $718.36       $775.4332   $775.43   $775.45   $775.50