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 $180.76   6.770%   $192.9975   $193.00   $193.00   $193.00  
  Purchase #2 $120.96   6.238%   $128.5055   $128.51   $128.50   $128.50  
  Purchase #3 $164.54   12.406%   $184.9528   $184.95   $184.95   $185.00  
  Purchase #4 $250.37   10.513%   $276.6914   $276.69   $276.70   $276.70  
  Purchase #5 $85.69   7.301%   $91.9462   $91.95   $91.95   $91.90  
  Purchase #6 $120.95   6.870%   $129.2593   $129.26   $129.25   $129.30  
  Purchase #7 $59.49   9.467%   $65.1219   $65.12   $65.10   $65.10  
  7 purchase totals = $982.76       $1,069.4746   $1,069.48   $1,069.45   $1,069.50