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 $236.73   13.779%   $269.349   $269.35   $269.35   $269.30  
  Purchase #2 $88.50   8.534%   $96.0526   $96.05   $96.05   $96.10  
  Purchase #3 $38.32   8.499%   $41.5768   $41.58   $41.60   $41.60  
  Purchase #4 $139.68   9.837%   $153.4203   $153.42   $153.40   $153.40  
  Purchase #5 $151.68   6.183%   $161.0584   $161.06   $161.05   $161.10  
  Purchase #6 $60.70   10.346%   $66.98   $66.98   $67.00   $67.00  
  Purchase #7 $58.54   5.839%   $61.9582   $61.96   $61.95   $62.00  
  7 purchase totals = $774.15       $850.3953   $850.40   $850.40   $850.50