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 $234.33   13.511%   $265.9903   $265.99   $266.00   $266.00  
  Purchase #2 $96.33   3.412%   $99.6168   $99.62   $99.60   $99.60  
  Purchase #3 $71.32   5.127%   $74.9766   $74.98   $75.00   $75.00  
  Purchase #4 $97.77   13.172%   $110.6483   $110.65   $110.65   $110.60  
  Purchase #5 $225.39   7.218%   $241.6587   $241.66   $241.65   $241.70  
  Purchase #6 $109.27   7.542%   $117.5111   $117.51   $117.50   $117.50  
  Purchase #7 $114.59   8.801%   $124.6751   $124.68   $124.70   $124.70  
  7 purchase totals = $949.00       $1,035.0769   $1,035.09   $1,035.10   $1,035.10