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 $239.83   5.461%   $252.9271   $252.93   $252.95   $252.90  
  Purchase #2 $117.73   5.529%   $124.2393   $124.24   $124.25   $124.20  
  Purchase #3 $181.41   7.252%   $194.5659   $194.57   $194.55   $194.60  
  Purchase #4 $21.88   12.192%   $24.5476   $24.55   $24.55   $24.50  
  Purchase #5 $198.99   9.828%   $218.5467   $218.55   $218.55   $218.50  
  Purchase #6 $160.97   8.580%   $174.7812   $174.78   $174.80   $174.80  
  Purchase #7 $34.26   7.850%   $36.9494   $36.95   $36.95   $36.90  
  7 purchase totals = $955.07       $1,026.5572   $1,026.57   $1,026.60   $1,026.40