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 $22.63   9.692%   $24.8233   $24.82   $24.80   $24.80  
  Purchase #2 $127.30   4.868%   $133.497   $133.50   $133.50   $133.50  
  Purchase #3 $74.28   13.107%   $84.0159   $84.02   $84.00   $84.00  
  Purchase #4 $183.60   13.484%   $208.3566   $208.36   $208.35   $208.40  
  Purchase #5 $111.66   3.834%   $115.941   $115.94   $115.95   $115.90  
  Purchase #6 $222.98   4.476%   $232.9606   $232.96   $232.95   $233.00  
  Purchase #7 $246.34   7.834%   $265.6383   $265.64   $265.65   $265.60  
  7 purchase totals = $988.79       $1,065.2327   $1,065.24   $1,065.20   $1,065.20