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 $61.60   11.581%   $68.7339   $68.73   $68.75   $68.70  
  Purchase #2 $152.97   4.347%   $159.6196   $159.62   $159.60   $159.60  
  Purchase #3 $130.26   11.787%   $145.6137   $145.61   $145.60   $145.60  
  Purchase #4 $240.40   9.109%   $262.298   $262.30   $262.30   $262.30  
  Purchase #5 $115.65   5.171%   $121.6303   $121.63   $121.65   $121.60  
  Purchase #6 $93.28   12.399%   $104.8458   $104.85   $104.85   $104.80  
  Purchase #7 $157.90   9.337%   $172.6431   $172.64   $172.65   $172.60  
  7 purchase totals = $952.06       $1,035.3844   $1,035.38   $1,035.40   $1,035.20