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 $65.43   4.512%   $68.3822   $68.38   $68.40   $68.40  
  Purchase #2 $22.82   5.636%   $24.1061   $24.11   $24.10   $24.10  
  Purchase #3 $173.79   5.826%   $183.915   $183.92   $183.90   $183.90  
  Purchase #4 $157.65   10.274%   $173.847   $173.85   $173.85   $173.80  
  Purchase #5 $228.55   5.617%   $241.3877   $241.39   $241.40   $241.40  
  Purchase #6 $239.43   5.461%   $252.5053   $252.51   $252.50   $252.50  
  Purchase #7 $196.47   8.413%   $212.999   $213.00   $213.00   $213.00  
  7 purchase totals = $1,084.14       $1,157.1423   $1,157.16   $1,157.15   $1,157.10