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 $59.75   8.838%   $65.0307   $65.03   $65.05   $65.00  
  Purchase #2 $8.66   13.802%   $9.8553   $9.86   $9.85   $9.90  
  Purchase #3 $150.40   3.116%   $155.0865   $155.09   $155.10   $155.10  
  Purchase #4 $191.83   3.542%   $198.6246   $198.62   $198.60   $198.60  
  Purchase #5 $87.80   6.853%   $93.8169   $93.82   $93.80   $93.80  
  Purchase #6 $107.73   8.194%   $116.5574   $116.56   $116.55   $116.60  
  Purchase #7 $220.96   9.799%   $242.6119   $242.61   $242.60   $242.60  
  7 purchase totals = $827.13       $881.5833   $881.59   $881.55   $881.60