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 $108.41   3.312%   $112.0005   $112.00   $112.00   $112.00  
  Purchase #2 $250.76   4.662%   $262.4504   $262.45   $262.45   $262.50  
  Purchase #3 $219.52   7.242%   $235.4176   $235.42   $235.40   $235.40  
  Purchase #4 $80.79   5.603%   $85.3167   $85.32   $85.30   $85.30  
  Purchase #5 $239.69   11.860%   $268.1172   $268.12   $268.10   $268.10  
  Purchase #6 $51.45   3.805%   $53.4077   $53.41   $53.40   $53.40  
  Purchase #7 $220.46   3.647%   $228.5002   $228.50   $228.50   $228.50  
  7 purchase totals = $1,171.08       $1,245.2103   $1,245.22   $1,245.15   $1,245.20