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 $53.40   5.797%   $56.4956   $56.50   $56.50   $56.50  
  Purchase #2 $141.48   5.144%   $148.7577   $148.76   $148.75   $148.80  
  Purchase #3 $86.48   11.805%   $96.689   $96.69   $96.70   $96.70  
  Purchase #4 $23.47   6.629%   $25.0258   $25.03   $25.05   $25.00  
  Purchase #5 $156.74   6.711%   $167.2588   $167.26   $167.25   $167.30  
  Purchase #6 $232.27   3.461%   $240.3089   $240.31   $240.30   $240.30  
  Purchase #7 $113.25   10.466%   $125.1027   $125.10   $125.10   $125.10  
  7 purchase totals = $807.09       $859.6385   $859.65   $859.65   $859.70