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 $68.99   8.821%   $75.0756   $75.08   $75.10   $75.10  
  Purchase #2 $221.48   8.246%   $239.7432   $239.74   $239.75   $239.70  
  Purchase #3 $89.76   3.157%   $92.5937   $92.59   $92.60   $92.60  
  Purchase #4 $164.94   5.273%   $173.6373   $173.64   $173.65   $173.60  
  Purchase #5 $136.49   12.441%   $153.4707   $153.47   $153.45   $153.50  
  Purchase #6 $24.94   8.163%   $26.9759   $26.98   $27.00   $27.00  
  Purchase #7 $237.93   10.791%   $263.605   $263.61   $263.60   $263.60  
  7 purchase totals = $944.53       $1,025.1014   $1,025.11   $1,025.15   $1,025.10