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 $38.80   12.399%   $43.6108   $43.61   $43.60   $43.60  
  Purchase #2 $166.51   9.284%   $181.9688   $181.97   $181.95   $182.00  
  Purchase #3 $136.32   10.305%   $150.3678   $150.37   $150.35   $150.40  
  Purchase #4 $196.54   12.381%   $220.8736   $220.87   $220.85   $220.90  
  Purchase #5 $114.89   5.346%   $121.032   $121.03   $121.05   $121.00  
  Purchase #6 $11.98   5.596%   $12.6504   $12.65   $12.65   $12.70  
  Purchase #7 $205.61   11.606%   $229.4731   $229.47   $229.45   $229.50  
  7 purchase totals = $870.65       $959.9765   $959.97   $959.90   $960.10