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 $104.26   9.326%   $113.9833   $113.98   $114.00   $114.00  
  Purchase #2 $138.46   6.722%   $147.7673   $147.77   $147.75   $147.80  
  Purchase #3 $135.28   3.220%   $139.636   $139.64   $139.65   $139.60  
  Purchase #4 $59.94   7.206%   $64.2593   $64.26   $64.25   $64.30  
  Purchase #5 $233.44   8.483%   $253.2427   $253.24   $253.25   $253.20  
  Purchase #6 $98.88   11.852%   $110.5993   $110.60   $110.60   $110.60  
  Purchase #7 $115.60   9.532%   $126.619   $126.62   $126.60   $126.60  
  7 purchase totals = $885.86       $956.1069   $956.11   $956.10   $956.10