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 $184.82   13.668%   $210.0812   $210.08   $210.10   $210.10  
  Purchase #2 $201.31   10.402%   $222.2503   $222.25   $222.25   $222.30  
  Purchase #3 $45.74   12.493%   $51.4543   $51.45   $51.45   $51.50  
  Purchase #4 $32.45   9.588%   $35.5613   $35.56   $35.55   $35.60  
  Purchase #5 $71.80   5.782%   $75.9515   $75.95   $75.95   $76.00  
  Purchase #6 $237.94   13.213%   $269.379   $269.38   $269.40   $269.40  
  Purchase #7 $159.35   3.177%   $164.4125   $164.41   $164.40   $164.40  
  7 purchase totals = $933.41       $1,029.0901   $1,029.08   $1,029.10   $1,029.30