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 $214.44   5.662%   $226.5816   $226.58   $226.60   $226.60  
  Purchase #2 $138.32   11.577%   $154.3333   $154.33   $154.35   $154.30  
  Purchase #3 $116.32   3.310%   $120.1702   $120.17   $120.15   $120.20  
  Purchase #4 $116.76   5.571%   $123.2647   $123.26   $123.25   $123.30  
  Purchase #5 $49.41   6.591%   $52.6666   $52.67   $52.65   $52.70  
  Purchase #6 $163.58   12.804%   $184.5248   $184.52   $184.50   $184.50  
  Purchase #7 $135.88   4.616%   $142.1522   $142.15   $142.15   $142.20  
  7 purchase totals = $934.71       $1,003.6934   $1,003.68   $1,003.65   $1,003.80