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 $130.63   8.579%   $141.8367   $141.84   $141.85   $141.80  
  Purchase #2 $126.33   9.760%   $138.6598   $138.66   $138.65   $138.70  
  Purchase #3 $122.99   4.283%   $128.2577   $128.26   $128.25   $128.30  
  Purchase #4 $222.49   11.559%   $248.2076   $248.21   $248.20   $248.20  
  Purchase #5 $151.76   12.332%   $170.475   $170.48   $170.50   $170.50  
  Purchase #6 $118.33   4.438%   $123.5815   $123.58   $123.60   $123.60  
  Purchase #7 $58.42   7.383%   $62.7331   $62.73   $62.75   $62.70  
  7 purchase totals = $930.95       $1,013.7514   $1,013.76   $1,013.80   $1,013.80