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 $146.46   4.482%   $153.0243   $153.02   $153.00   $153.00  
  Purchase #2 $240.93   8.752%   $262.0162   $262.02   $262.00   $262.00  
  Purchase #3 $169.66   8.476%   $184.0404   $184.04   $184.05   $184.00  
  Purchase #4 $63.39   13.245%   $71.786   $71.79   $71.80   $71.80  
  Purchase #5 $87.34   12.647%   $98.3859   $98.39   $98.40   $98.40  
  Purchase #6 $107.44   3.231%   $110.9114   $110.91   $110.90   $110.90  
  Purchase #7 $175.48   8.129%   $189.7448   $189.74   $189.75   $189.70  
  7 purchase totals = $990.70       $1,069.9090   $1,069.91   $1,069.90   $1,069.80