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 $64.41   11.273%   $71.6709   $71.67   $71.65   $71.70  
  Purchase #2 $249.49   10.861%   $276.5871   $276.59   $276.60   $276.60  
  Purchase #3 $225.76   8.867%   $245.7781   $245.78   $245.80   $245.80  
  Purchase #4 $39.70   11.385%   $44.2198   $44.22   $44.20   $44.20  
  Purchase #5 $198.43   3.608%   $205.5894   $205.59   $205.60   $205.60  
  Purchase #6 $240.64   9.420%   $263.3083   $263.31   $263.30   $263.30  
  Purchase #7 $142.43   6.599%   $151.829   $151.83   $151.85   $151.80  
  7 purchase totals = $1,160.86       $1,258.9826   $1,258.99   $1,259.00   $1,259.00