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 $40.83   9.475%   $44.6986   $44.70   $44.70   $44.70  
  Purchase #2 $117.90   11.126%   $131.0176   $131.02   $131.00   $131.00  
  Purchase #3 $157.93   6.800%   $168.6692   $168.67   $168.65   $168.70  
  Purchase #4 $170.94   13.577%   $194.1485   $194.15   $194.15   $194.10  
  Purchase #5 $250.41   13.289%   $283.687   $283.69   $283.70   $283.70  
  Purchase #6 $216.57   11.527%   $241.534   $241.53   $241.55   $241.50  
  Purchase #7 $112.52   3.556%   $116.5212   $116.52   $116.50   $116.50  
  7 purchase totals = $1,067.10       $1,180.2761   $1,180.28   $1,180.25   $1,180.20