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 $56.35   8.711%   $61.2586   $61.26   $61.25   $61.30  
  Purchase #2 $219.65   12.227%   $246.5066   $246.51   $246.50   $246.50  
  Purchase #3 $129.42   13.200%   $146.5034   $146.50   $146.50   $146.50  
  Purchase #4 $122.78   10.814%   $136.0574   $136.06   $136.05   $136.10  
  Purchase #5 $127.79   9.830%   $140.3518   $140.35   $140.35   $140.40  
  Purchase #6 $163.28   6.255%   $173.4932   $173.49   $173.50   $173.50  
  Purchase #7 $210.63   10.535%   $232.8199   $232.82   $232.80   $232.80  
  7 purchase totals = $1,029.90       $1,136.9909   $1,136.99   $1,136.95   $1,137.10