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 $65.82   8.260%   $71.2567   $71.26   $71.25   $71.30  
  Purchase #2 $189.68   4.571%   $198.3503   $198.35   $198.35   $198.40  
  Purchase #3 $235.96   12.450%   $265.337   $265.34   $265.35   $265.30  
  Purchase #4 $175.51   3.510%   $181.6704   $181.67   $181.65   $181.70  
  Purchase #5 $68.33   3.382%   $70.6409   $70.64   $70.65   $70.60  
  Purchase #6 $215.51   10.796%   $238.7765   $238.78   $238.80   $238.80  
  Purchase #7 $119.76   3.120%   $123.4965   $123.50   $123.50   $123.50  
  7 purchase totals = $1,070.57       $1,149.5283   $1,149.54   $1,149.55   $1,149.60