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 $244.27   10.337%   $269.5202   $269.52   $269.50   $269.50  
  Purchase #2 $192.43   4.869%   $201.7994   $201.80   $201.80   $201.80  
  Purchase #3 $170.41   12.572%   $191.8339   $191.83   $191.85   $191.80  
  Purchase #4 $57.91   11.561%   $64.605   $64.61   $64.60   $64.60  
  Purchase #5 $49.29   12.388%   $55.396   $55.40   $55.40   $55.40  
  Purchase #6 $62.59   13.664%   $71.1423   $71.14   $71.15   $71.10  
  Purchase #7 $249.99   12.412%   $281.0188   $281.02   $281.00   $281.00  
  7 purchase totals = $1,026.89       $1,135.3156   $1,135.32   $1,135.30   $1,135.20