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 $60.34   13.637%   $68.5686   $68.57   $68.55   $68.60  
  Purchase #2 $218.77   4.516%   $228.6497   $228.65   $228.65   $228.60  
  Purchase #3 $150.26   10.391%   $165.8735   $165.87   $165.85   $165.90  
  Purchase #4 $42.70   4.476%   $44.6113   $44.61   $44.60   $44.60  
  Purchase #5 $123.30   12.638%   $138.8827   $138.88   $138.90   $138.90  
  Purchase #6 $107.57   6.827%   $114.9138   $114.91   $114.90   $114.90  
  Purchase #7 $130.30   8.180%   $140.9585   $140.96   $140.95   $141.00  
  7 purchase totals = $833.24       $902.4581   $902.45   $902.40   $902.50