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 $38.98   11.869%   $43.6065   $43.61   $43.60   $43.60  
  Purchase #2 $218.65   10.597%   $241.8203   $241.82   $241.80   $241.80  
  Purchase #3 $239.70   3.570%   $248.2573   $248.26   $248.25   $248.30  
  Purchase #4 $150.95   8.444%   $163.6962   $163.70   $163.70   $163.70  
  Purchase #5 $235.54   13.838%   $268.134   $268.13   $268.15   $268.10  
  Purchase #6 $198.66   11.657%   $221.8178   $221.82   $221.80   $221.80  
  Purchase #7 $5.57   12.343%   $6.2575   $6.26   $6.25   $6.30  
  7 purchase totals = $1,088.05       $1,193.5896   $1,193.60   $1,193.55   $1,193.60