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 $216.45   10.757%   $239.7335   $239.73   $239.75   $239.70  
  Purchase #2 $201.82   12.857%   $227.768   $227.77   $227.75   $227.80  
  Purchase #3 $39.99   11.376%   $44.5393   $44.54   $44.55   $44.50  
  Purchase #4 $239.53   5.808%   $253.4419   $253.44   $253.45   $253.40  
  Purchase #5 $82.78   3.426%   $85.616   $85.62   $85.60   $85.60  
  Purchase #6 $33.84   9.205%   $36.955   $36.96   $36.95   $37.00  
  Purchase #7 $71.78   11.502%   $80.0361   $80.04   $80.05   $80.00  
  7 purchase totals = $886.19       $968.0898   $968.10   $968.10   $968.00