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 $43.76   13.249%   $49.5578   $49.56   $49.55   $49.60  
  Purchase #2 $150.67   10.806%   $166.9514   $166.95   $166.95   $167.00  
  Purchase #3 $179.43   7.321%   $192.5661   $192.57   $192.55   $192.60  
  Purchase #4 $105.90   8.382%   $114.7765   $114.78   $114.80   $114.80  
  Purchase #5 $70.70   11.460%   $78.8022   $78.80   $78.80   $78.80  
  Purchase #6 $209.43   7.824%   $225.8158   $225.82   $225.80   $225.80  
  Purchase #7 $235.64   12.869%   $265.9645   $265.96   $265.95   $266.00  
  7 purchase totals = $995.53       $1,094.4343   $1,094.44   $1,094.40   $1,094.60