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 $121.69   8.137%   $131.5919   $131.59   $131.60   $131.60  
  Purchase #2 $34.41   3.310%   $35.549   $35.55   $35.55   $35.50  
  Purchase #3 $154.45   7.293%   $165.714   $165.71   $165.70   $165.70  
  Purchase #4 $126.25   13.826%   $143.7053   $143.71   $143.70   $143.70  
  Purchase #5 $215.72   4.137%   $224.6443   $224.64   $224.65   $224.60  
  Purchase #6 $124.81   4.582%   $130.5288   $130.53   $130.55   $130.50  
  Purchase #7 $240.74   9.648%   $263.9666   $263.97   $263.95   $264.00  
  7 purchase totals = $1,018.07       $1,095.6999   $1,095.70   $1,095.70   $1,095.60