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 $108.78   10.256%   $119.9365   $119.94   $119.95   $119.90  
  Purchase #2 $243.42   6.126%   $258.3319   $258.33   $258.35   $258.30  
  Purchase #3 $189.83   12.861%   $214.244   $214.24   $214.25   $214.20  
  Purchase #4 $101.62   6.296%   $108.018   $108.02   $108.00   $108.00  
  Purchase #5 $245.70   10.467%   $271.4174   $271.42   $271.40   $271.40  
  Purchase #6 $139.25   6.158%   $147.825   $147.83   $147.85   $147.80  
  Purchase #7 $41.38   6.500%   $44.0697   $44.07   $44.05   $44.10  
  7 purchase totals = $1,069.98       $1,163.8425   $1,163.85   $1,163.85   $1,163.70