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 $58.59   4.588%   $61.2781   $61.28   $61.30   $61.30  
  Purchase #2 $216.44   4.476%   $226.1279   $226.13   $226.15   $226.10  
  Purchase #3 $22.89   8.349%   $24.8011   $24.80   $24.80   $24.80  
  Purchase #4 $109.39   4.731%   $114.5652   $114.57   $114.55   $114.60  
  Purchase #5 $222.45   3.173%   $229.5083   $229.51   $229.50   $229.50  
  Purchase #6 $92.79   8.869%   $101.0195   $101.02   $101.00   $101.00  
  Purchase #7 $226.64   3.161%   $233.8041   $233.80   $233.80   $233.80  
  7 purchase totals = $949.19       $991.1042   $991.11   $991.10   $991.10