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 $76.76   12.519%   $86.3696   $86.37   $86.35   $86.40  
  Purchase #2 $144.68   4.636%   $151.3874   $151.39   $151.40   $151.40  
  Purchase #3 $45.30   12.629%   $51.0209   $51.02   $51.00   $51.00  
  Purchase #4 $39.29   7.632%   $42.2886   $42.29   $42.30   $42.30  
  Purchase #5 $193.40   6.252%   $205.4914   $205.49   $205.50   $205.50  
  Purchase #6 $178.99   7.847%   $193.0353   $193.04   $193.05   $193.00  
  Purchase #7 $213.36   11.774%   $238.481   $238.48   $238.50   $238.50  
  7 purchase totals = $891.78       $968.0742   $968.08   $968.10   $968.10